Her plan was always "cope with her family's bullshit until she could go off to college." She would need scholarships for that, but she's smart, and more importantly, determined. And that's still the plan, sort of. But it's come to her attention more and more, lately, that potential maybe scholarships in the future are unhatched eggs, and that one shouldn't count the chickens in them.
And her parents are getting less and less bearable to deal with as she gets older. Her brother's...fine. Mostly. Except that he doesn't want to cut ties with their parents, which limits the extent to which she can keep ties with him, in the long run. She can probably hang on until she turns eighteen; even if she doesn't manage to get into college, she can still leave.
But she doesn't want to if she doesn't have to.
She looks into the ways to emancipate herself as a fifteen-year old.
One way is to get married, which--ugh, her mother might actually approve of that one, but even if there's any overlap between the kind of husband Rhonda would be willing to have and the kind her mother would want for her, he hasn't presented himself to her yet. One way is with mutual consent from her parents, which, haha, no. One way is to join the armed forces, which, extra, special, no.
One way is to become a magical girl.
Probably her odds aren't great. But it would be a good thing for a variety of other reasons besides just getting her out of here three years early, so she might as well check out what the application looks like.