Jennifer Walters is not putting up with her guardians one more day.
She's sick of this overcrowded shack in the Colorado woods. She's sick of the way her uncle's yelling makes her cousin Bruce shrink into himself, and the way her aunt's consistent disappointment makes him forget his own abilities. She's sick of of the threat of going without dinner if she doesn't get her chores done. She's sick of her father's rants about "genetic purity" and "Anglo-Saxons" and "damn mutants" and some people being better than others because of the color of their skin.
But worse than all of that is the conversation she overheard between her father and her uncle. The conversation where they talked about how Bruce and Jennifer are "the two purest kids they know" and how, when they're older, they should marry each other, have kids with each other, rather than "mix their blood" with anybody else. That is absolutely not an option, and neither is staying under the same leaky roof as someone who's planning to insist on it.