Why is the film titled 'Frances Ha'?

Here's an article with an interview with the film's director Noah Baumbach. His first feature-length film, "Kicking and Screaming" shares a title with a Will Ferrell movie that he's not overly fond of. There is a Jessica Lange film already named "Frances" and he didn't want his film to be confused with it.

Was that annoying when that movie came out with the same title?
Yeah. It was very annoying. The same year, "Crash" came out, too -- or right around there -- I imagined David Cronenberg was annoyed as well. I mean, actually, that was something that I was very conscious about because an obvious title for our movie was "Frances." And there's a very good movie with Jessica Lange called "Frances" about Frances Farmer. It kind of pushed Greta and me to get more inventive with the title and, ultimately, I think to come up with a kind of great ending for the movie. So, I wish the filmmakers of "Kicking & Screaming" had maybe done similar -- [laughs] worked a little harder to figure it out.

In addition to the above answer, the title is also obviously a play on words:

'Frances Ha' could be pronounced as Francesca, which is the common development of Frances. The character is Happy-Go-lucky, naive and largely oblivious to the political, 'daddy-funded' mechanics of the dance world she works in, but perseveres regardless.

The 'Ha' could be seen as a play on her name, and an triumphal refusal to give in.

When she folds the label, she defines and claims her adult identity. She has her own apartment, she appreciates her relationships but she isn't defined by them, she has work and an artistic identity. She owns herself, and she defines herself independently. She isn't her friend's Frances, or her parent's last name, or undateable. She's Frances Ha. It's the culmination of her search for a self, she's finally embracing her character as is.

I see it as code for "Frances Undatable", due to use of the phrase "Ha Ha" in the movie after a character says that