Why isn't she instead studying for her exams or volunteering for charity work?
You read a book about adventurers. Why the act of doing so is praised, and not the act of hard work in fields or mills?
The real answer to those questions is that it makes the story more interesting. You are searching for a political reason where there is none. The question "what makes a story interesting" is philosophy and writing and not politics.
Personally I powered through some boring-but-virtuous books in my youth, but now I'm a middle-aged adult with less free time, I've realised reading is supposed to be fun.
So if a book review tells me a book is virtuous without telling me if it's fun, that book review isn't much use to me.
> Why isn't she instead studying for her exams or volunteering for charity work?
Because that isn't the story the author came up with?
Everything involving a substantial agreement or disagreement between persons is politics, that's what it means. Claiming that something 'should not be political' is almost always an assertion that your position is unassailably correct.
No, it it's an assertion that there's a whole world beyond your conception of "politics" and your position is impoverishing of the human experience.
Although the first sentence "YA about young heroine rebelling" is itself about politics really, so my comment doesn't apply.
Authors write what they feel like writing and what readers feel like reading, not what some liberal arts professor wants to include in their "the politics of YA books" course. Let me assure you that neither the writer nor the reader are interested in your concerns.