Good question! Her backstory doc mentions that she "decided to become trans on an impulse, seeking to love herself and find some semblance of say in her life in a manner her parents could not", but let's look into that a little bit.
Faithe's parents were shitty.
Not, like, physically abusive rotten-to-the-core types, just really not there for her emotionally. Their intent of shoving her into a life of business careership was born from any parent's desire to see their offspring live comfortable lives, tunnel-visioned and twisted into something horribly negligent towards fostering a sense of self.

And when you compact this into a girl who didn't want to be this but had no say in the manner, you grow dissatisfied with yourself. You want to be a version of yourself you like, so you gotta make small steps towards being that.
And Faithe did that. She liked the idea of being a girl better, and that was that. Her parents accepted it and it was the only good thing they ever did. (even if it was with placation in mind)