From an MTV interview with the writer, Damon Lindelof:

Question:

We talked a bit about David but let's concentrate on Vickers for a second if we could. Like David, her motivations remain mysterious for much of the film. And certainly her resemblance (look, icy mannerisms) to David is interesting to say the least. Janek asks the question directly so I shall as well. Is she a robot?!?

Answer:

Vickers. Yes, she does look like David. Yes, this was intentional. What better way to piss off your daughter than to build the male equivalent of her? But enough about daddy issues (seriously, Lindelof, we get it!), allow me to answer your question. Is she a robot? She is not.

To address the points brought up more specifically though...

Peter Weyland, the old trillionaire, did say that she was his daughter. He could have meant this figuratively though.

He calls David "the closest thing [he has] to a son." If he sees androids as his figurative children, it would seem odd for him to see David as only being "close to a son".

Janek, the captain of the Prometheus, asked Vickers for sex like he was asking an android for a glass of water. After she agreed without emotion, he sang "if you can't be with the one you love, love the one you're with" before he had sex with her (although they didn't show it). This suggested to me that he wasn't going to be with a human, but was going to love the android he was with.

Janek is on a multi-year mission away from home and presumably away from his family. The other less devious conspiracy-filled theory is that he's lamenting the fact that he's away from his actual lover (wife, girlfriend, whomever). If he can't be with his true love, for whatever reason, he may as well love the one he's with. In this case, he had two female options: Shaw and Vickers. Since Shaw was in a committed relationship with another person on board, Vickers makes a little more sense.

The surgery pod wasn't designed for use by a woman. Why would a trillionaire who could afford to build a surgery pod not build one for use by his own daughter?

Weyland has demonstrated that he has no particular love for his daughter. He is an egotistical man whose aims are centered solely around himself. The surgery pod was also not set up for Shaw, who was arguably a more instrumental crew member than Vickers. The pod was intended for his own personal use.

Vickers has a different last name than Weyland, which at least suggest that they are not natural father-daughter.

Plenty of children have different last names from their fathers - regardless of biology. Many even have the same last name even though they are not biologically related. This argument holds no weight.

She is clearly not an android:

• She answered "yes" to having sex, to prove her humanity.
• An android would not have argued with its creator.
• An android would not have had the option to either come with its creator or stay behind and manage a company.
• An android would not have been awakened from stasis as it would not age and not be put in stasis.
• An android would not require a life pod.
• An android would not set fire to a person infected with a disease rather than allowing them upon a spaceship. It would not be vulnerable to disease.

It's never revealed if Vickers is indeed an android.

Therefore, it's up to the viewer to decide.I'm also guess she would be a android.

• Age Issue:

  Weyland seems he aged like 100+ and too old to be her father, with Vickers being too young to be his daughter. She may call Weyland father in the same way David refers to Weyland as "father", in the sense that she was made by and serves Weyland.

• Relationship of David and Vickers':

  David calls Meredith his "mother." If both were androids created by Weyland and Meredith was David's predecessor.

• Vickers last name Issue:

  Meredith's last name is Vickers, So there is no possibility that she's Weyland's daughter.

• Meredith's death is not shown:

  If she were attacked by an alien, her blood (or lack of it) would be definitive evidence as to whether or not she was an android. Instead, her death seems intentionally ambiguous.

• Surgery pod:

  The surgery pod configured only for men, so it's suggesting that she doesn't need medical assistance.

According to IMDB,

Evidence for the android theory;

1. She calls Weyland "Father," but in a sardonic tone. Weyland seems too old to be her father, with Vickers being too young to be his daughter. She may call Weyland father in the same way David refers to Weyland as "father", in the sense that she was made by and serves Weyland.
2. Vickers also appears to throw David against the wall with ease, which would seem strange if Vickers is indeed human. We see in Alien how hard it is to physically move an android; when Ash attempts to kill Ripley it takes two people to stop and restrain him.
3. The surgery-module in her escape pod only performs operations on males, as shown when Shaw attempts to perform a cesarean section; odd considering the point of such a device would be to heal injuries inflicted on Vickers or the entire crew (or possibly just for Weyland), suggesting that she doesn't need medical assistance.
4. While Vickers sleeps in a cryo-chamber for the trip and David doesn't; we are shown Ash in Alien to sleep in a cryo chamber as well; Ash was masquerading as human and so Vickers may have been doing the same, especially if she is there to carry out the will of Weyland discreetly. Sleeping in a cryogenic chamber would be good cover and would remove any suspicion. 5.She shows little or no emotion at the death of Weyland, although he is supposedly her father.

In my mind, it's likely that Vickers is an android.

• The first clue while watching the film was her quick recovery from cryosleep.
• Later she's called Weyland's daughter, but David was given the name Weyland "had initially reserved for his own human son".
• Vickers has the physical strength to easily push David around. In Alien, androids are depicted as being much stronger than humans, so this suggests Vickers is as strong as David, an android.
• David and Vickers were the only ones who knew that Weyland was on board, so Weyland trusted them both completely. We know why he trusted David, it doesn't seem outlandish that he trusted Vickers for the exact same reason.
• The med pod is in Vickers quarters but would be unable to properly perform surgery on her, given that it's set to male. If she were a human, it's possible that Weyland didn't care enough for Vickers to provide her with the medical capabilities that the med pod provided.

My own theory is that Vickers is a later model of android than David. David's (a male, mind you) a logical breakthrough who can imitate human emotions. Then for a later model, a female android is created who has actual emotions. This provides a sort of symbolical balance in Weyland's ultimate creation, artificial men and women. This also makes a nice biblical reference.

My biggest reason besides the cryosleep that indicates she is an android is the design. David has the yellow hair and wears shades of cool blue and cool gray that is also tied into the ship's design. Meredith likewise has the same color scheme. They are both hardware just like the ship. She walks like David. She is strong like David, and she doesn't display human compassion like when she burns up Charlie (Elizabeth tells David her compassion is the reason that she is human and he isn't). There will be those who say, what about the other scientists who had blonde hair? But those scientists were seen yacking after cryosleep or slumped over; and they weren't given the prominence Meredith was given. Meredith wasn't.

Furthermore, the subtext in the film is that David knows she is an android and she doesn't know it, just like Rachael in Blade Runner. David gets a kick out of her trying to establish her human superiority over his robotic inferiority (when she threatens to cut his cord) because he has intimate knowledge of her fabrication. The look on his face is that he wants to tell her but his orders prevent it. When we see David getting his orders from Weyland about "Try harder" -- it was evident by the skewn composition that we were seeing it from someone else's point-of-view. But the point of view was detached and withdrawn.

Also, it involved a level of stealth that clearly verged on predatory or suprahuman. Then the revelation was that Charlize Theron was the individual who had snuck up on him and was watching him. When is a human character in a Ridley Scott film ever able to sneak up on a non-human character in such a predatory way unless it was alien or android? In this scene, the power is clearly Charlize Theron's. Not just in her actions but in the way Scott codes her as a silent stealthy creature. It's clear that David and Meredith are related in ways the others are not related because their movement, their mannerisms, and their attitudes are synchronized. As actors, they are playing off each other, so Theron tries to humanize Meredith in a way that is far more advanced than David.

Lastly, we can see the expressions in Weyland's face that when she tries to use emotional pleas for him not to go and see the Giant, that her emotional pleas ring hollow. Firstly, it's the way she says father -- though it's an appeal to emotion, it is awkwardly uttered and awkwardly timed. She was directed to say the line as if it lacked proper emotion. As if it were the thing to say. Only a machine that lacked emotion but were trying to find a way to make an emotional appeal based on its programming would do so in such an apathetic manner. Weyland's physical reaction is that her appeals ring hollow because he knows she is a hollow woman at her core. Far more advanced and emotionally sophisticated but not sophisticated enough. Some argue that Weyland's quest for eternal life from the Giants might be motivated by his dream to create an emotionally exact replica of human life in the form of a robot. So although Theron is far more advanced than David, she still has room for refinement. That her last name is Vickers is simply Weylan'ds way of giving her an additional level of identity separate from David's.

On an exegetical note -- whenever a magician says pay not attention over here, then there's something there that he really wants you to see, and it's a form of reverse psychology in the art of misdirection. Likewise, the text tried to dismiss the question of whether or not that she was an android in such an obvious way that it was like c'mon 97% of what I have seen codes her as an android, and you want me to place that 3% in the form of dialogue over what my eyes have seen? I'm sorry, people lie with their words all the time; I will trust my eyes.

I don't buy Lindelof's answer. Scott supercede's Lindelof as a director. The history of his work indicates that Meredith is an android. He codes her as such, frames her as such, has her walk and talk and posture as such. She moves silently as such. She could be the Terminatrix. If she were definitely human, than ambiguity would not be necessary. If she were android, ambiguity is understandable. I think Scott is smarter than that. So my answer is yes, she is an android. Until Scott himself says 'no.' If she is not an android, then I will be the first to admit that I was wrong. But I don't see why a smart director allows for that level of ambiguity. I think she is in such denial of her robotic nature that she needs to prove her humanity. Having sex does not mean she is not an android. Androids have simulated sex in Scott's films before. And David could be the android that does his physical (dark bidding), and Meredith could be the one that does his corporate bidding. He can use them as different aspects of his will seeing as how a man with secrets like himself can't trust anything he can't control.

Meredith Vickers is not an android. The reasons are:

1. She died in the movie by the crushing spaceship. If she was an android she could never die like David.

2. When Meredith meets with Weyland she calls him "father".

   Weyland: "Anything else?"

   Mederith: "No, Father!"

   Now an android may also call its creator "father," but an android does not feel anxiety for his creator and sob like Meredith did after the scene. On the other hand David, an android, never cries. To him an order is an order.

3. Remember the conversations between the captain and Meredith in the movie:

   Captain: You know if you really wanna get laid, you really don't have to pretend to be interested in Pyramid scan. You could just say, "Hey, I'm trying to get laid."

   Mederith: I could. I could say that, right? But it wouldn't make sense why I would fly myself half a billion miles from every man on Earth if I wanted to get laid, would it?

   Captain: Hey Vickers, I was wondering, are you a robot?

   Meredith (With an inviting smile): My room....10 minutes.

   This sequence clearly indicates that the Captain tried to mock Meredith with "Are you a robot"? To which Meredith invited him for "sex". Androids don't do sex.......Does David?

4. Androids don't need life-support systems...like she needed.

5. Androids also don't burn an infected body if not instructed.

6. Her body strength may be nearly the same as David because surely she made herself strong enough like David as she must be angry with him because of her father's fondness for him over her. Another logic can also be that when she pushed him he was not at all ready for the attack, and also David would not attack the creator's own daughter!

7. Also the cold nature of her father must push her into being cold. But that does not make her an android.

Think like a writer..not like the story is real as one post did.

SHE IS WITHOUT A DOUBT A ROBOT. We know this through the writing technique used. There is no point in having David expound so heavily on the fact that he was wearing the hazard suit for "show" if there was not another character also wearing one for show. You write this dialog in the script only to explain ALL of the hidden robots behavior--which is obviously Vickers. Your not suppose to know this---but you are suppose to recall what David said when Vickers is exposed and you object. The audience will recall the pretending to be human lines and it will explain why you didnt see it. It extremely common technique in mystery. In fact as soon as these lines were spoken I knew there was another robot and no more than a minute went by when she was called a robot by the captain. I am almost certain there were scenes cut at the end that show it. As soon as our star's hazard mask broke --I think Vickers broke too and she was going to be able to survive but it was saved for the next movie. Either way, that scene is coming as all dialog and actions point to it.

I'll add my 2 cents that the conversation with the ship's captain makes it clear that she is not an android. Androids are not mysterious at this point in time -- most people, certainly a technocrat like a star ship's captain, know about androids and Vickers implied that having sex (in ten minutes which is also significant -- why would an android need to prepare for sex) would prove that she was not.

On the other hand, they could make an android that could have sex -- that hardly seems difficult at all -- so I don't know why having sex would prove her humanity except that apparently it would or the captain would have responded differently.

I note also that David behaves roboticaly although Ash was able to successfully fool humans into believing he was human, even eating. Vickers acted pretty human and I don't even know why the captain would jokingly ask her. Incredibly disrespectful behavior towards the owner of the trillion buck ship and at that point he still was very much an employee who no doubt wanted to keep a job that probably paid the equivalent of many millions per year -- I could see that once things started to fall apart discipline would also crumble but no one had died yet when they had their little flirtation and after people started to transform into monsters I doubt that sex would arise. It is a sort of strange movie -- they see what has happened to one of their crew mates, he became a monster and killed several people but then they sort of return normal. I note also that Shaw has removed a monstrous "embryo" from her own body and says nothing about this to anyone, she just joins the party going to meet the Engineer and keeps mum about yet another horrible thing that has happened.