But if she's a youkai fox she should be able to use transformation magic, right?
Depends on how magic works in this world. If she has to constantly maintain it, she'd have to be living the lie only in short burst. Also even if she could keep it constant, there is her own self esteem. Deep down she would know it's not her real self.
kinda like Clay face in Batman. He "can" be human if he wants. But he has to keep focusing to maintain a transformation. The moment he relaxes he goes back to being a puddle of mud. It would be to tiring to maintain such a transformation 24/7.
I am sorry to tell you, but according to the test results...
You have a predisposition towards Loli-Hagitis.
"Loli babaa" (lolihag) roughly means "child-looking granny", slang used to describe the body type of people/humanoids/beings/etc. who look like little girls despite being very old. Fictional fox girls often get hit with this.