Quote 1
I am proud. It will get me into trouble someday, but today it makes me brave. I walk toward the ledge and hear snickers behind me. (6.66)
Tris has lots of "I am" moments in the book. Usually she's saying she's not selfless enough to be Abnegation or she's so brave she should be Dauntless. But check out here, when she identifies as proud. But there's no faction for pride. Or is there? Notice that the Dauntless get called proud a bunch (13.9, 24.50).
Quote 2
"Um..." I don't know why I hesitate. But "Beatrice" just doesn't sound right anymore.
"Think about it," he says, a faint smile curling his lips. "You don't get to pick again."
A new place, a new name. I can be remade here.
"Tris," I say firmly. (6.82-5)
This is a big moment, which Tris helps us recognize with that little thought in the middle: this isn't just "I can pick a new name." This is "I can be remade." That's an awful lot of work for a nickname. (And are Tris and Four the only peeps with nicknames?)
Quote 3
I look at my reflection in the small mirror on the back wall and see a stranger. She is blond like me, with a narrow face like mine, but that's where the similarities stop. I do not have a black eye, and a split lip, and a bruised jaw. I am not as pale as a sheet. She can't possibly be me, though she moves when I move. (11.9)
If you wanted to do a paper on identity and material goods, you might want to look at mirrors in this book, mostly because Tris doesn't have Facebook. After some time with the Dauntless, Tris doesn't recognize herself, probably because she's still holding on to her old self-image as meek Abnegation girl.