Dunno how you could say for sure anything before, especially since back then we didn't know even the little we know now. We still don't know if working under her uncle was the only chance for a decent life she could see, or if it was just to satisfy her ambition. Apparently she does have a pressing reason, but wouldn't most have in a school whose aim is to train strong fighters and pit them against each other and those from other schools? It's not exactly just like a normal high school, which would mostly be a step toward the next form of education or even just a regular job for those not interested in schools.
I'm sure she actually would have a real alternative or a few with her skills and potential, but she's too young and shy to try to find them. It didn't seem to me like the uncle was specifically blackmailing her. It looked more like by helping him she was helping herself.