[it's not an unfair question, and she doesn't seem bothered by it.]

Because it's a very personal thing, I think. When a magical girl makes a contract back home, she agrees to fight in exchange for a wish — she's choosing to trade having a normal life for something she really wants to come true.

[she didn't know what the consequences really were, though — a magical girl rarely does. or, maybe she did? memories are another rather sore subject, but that's something she's keeping much more closely guarded.]

You could say that becoming a magical girl is something that someone does out of hope.