Why Did Starbuck Grab the Ejection Handle?

There is no direct explanation for her immediate reaction, perhaps it ties into the feeling of what she believes she should do in relation to her counterpart, Pythia who was sentenced to die on a pyre, but actually died in the 13th tribes escape featured more in The Final Five comic Book?

Pythia was an ancient oracle, believed to have been one of the writers of the Sacred Scrolls, some 3,600 years prior to the events of the Miniseries and the destruction of the Twelve Colonies of Kobol.

Pythia's writings are both obscure and yet well-known: obscure, in that her entire writings are not widely studied among modern Colonials, but well-known in that extracts are widely quoted, often out of context, such as the following:

"All this has happened before. All this will happen again."1 Key to Pythia's writings are two passages, relating to the exile and rebirth of the human race:

"And the Lords anointed a leader to guide the caravan of the heavens to their new homeland. And unto the leader, they gave a vision of serpents, numbering two and ten, as a sign of things to come."

More interesting however, is that Kara's experience in relation to the Nebula is presented in three ways:

1. Lee's perspective: Kara goes into the nebula, she tries to eject, but ultimately he sees her and the viper explode.

2. Kara's perspective: Kara went through the Nebula, went to Earth (1) and came back.

3. In the season 4 episode, Sometimes a Great Notion, Kara finds her burned body and viper on Earth (1) and is confused.

IMO the point of the variations is to play on two aspects of the metaphysical:

1. Spiritual: Battlestar Galactica is a Space Opera with heavy spiritual leanings, in which we come to understand there is something "greater than" the characters, controlling fate in the universe(s). The idea then could be seen as allegorical to a "3 in 1" transformation-like concept, since Kara is considered a kind of "Angel" in the BSG mythos. (This is also furthered by Zoe Graystone in Caprica prequel through Zoe A: virtual, robot, skin-job Zoe, and Messenger Zoe).
2. To explain that in science-fiction terms, the Nebula then acts as a plot device for temporal anomaly, time-travel, and/or could indicate a subtext for the possibility of multiple universe. In addition the concept of the Law of Averages is an equivalent to Cycle Cosmology.

Note: There are other character that should of died in explosions and find some way to exist beyond themselves: Dr. Gaius Baltar (BSG Pilot) and in prequel series Caprica with Zoe Graystone living on through the virtual Zoe & Messenger Zoe and Tamara Adama who somehow also has a virtual avatar.

In addition many characters are seen detonating bombs throughout both series, so ejecting into a hot burning Nebula could be seen in similitude to a-hand- on-a-bomb-detonator and therefore, could be seen as a thematic motif.