Except she already has a backstory. A major, if not the major, defining point of her would be personality was already laid out before us. Born with no parents, with no childhood, and our future set in stone- to fight until we die.
Choices are fine, but only so long as they remain consistent with the already presented narrative. Some of them fit to a degree: Meek, Rebellious, or Doubtful? Sure, each fit in in their own way with a regimented secret government project raising a young girl that's more weapon than human to most if not all of them.
*Shrug* If you can make them fit, good on you I guess.