That mage bastard. Surely many nobles want to become mages, I can imagine and there is this enthusiastic noble girl all smiles ans stuff and I can imagine it pissed him of to be bound to a child, that believed magic is fun, while it is hard work for him. Even though she IS a genius! Knowing those kind of stories, I bet he just told her a load of bullshit, over loaded her worklimit with senseless exercises, was frustrated bottomless, when she didn't quite and in the end, when she miraculously somehow managed to evoke magic, becasue she made some sense from the scraps of real knowledge she accumulated and got hurt, he really cursed her, said bullshit to scare her and told her parents she doesn't have any talent.
The sad thing is, I believe, if she would have studied on her own she would have seen through it. She should have believed that bastard.