Either this is just a phase of her adolescence that she will look back on later as the time when she felt most comfortable as a fox OR this will continue to hold meaning as an enduring identity.
Both of these seem plausible. It's really common for autistic children to feel like they are aliens or fairies or robots because they feel fundamentally different.
Either way what's the harm other than "some people will reject you for being different" (something she ALREADY experiences)?