What do you mean? She can go all out as far as being a human is concerned, it just takes more effort than it's generally worth and it's only temporary. Her eyes, her ears, her tail, that's all as "proof of what she is".
The thing to her right on the otherhand is a sexless kitsune that gets off on manipulating people by swapping genders.
Kuu... just kind of sits there complaining. Sure she comes through in a pinch, but while a certain other *human* character takes levels in badass she just kind of stagnates.
Horo, on the other hand, sits there complaining for a bit, then stands up, and visits pain upon the wicked. Or the poor SOBs unlucky enough to be between her and the honey peaches.