I agree. She would be the guiltier of the two parties in that case. I guess I would feel bad about beating a female, but no so bad about beating on another dude (even if she deserves it more). In reality, I would personally do neither - but I'm sure the thought would cross my mind several times over.
Hypocrytical as it may be, I would imagine that it could get hard to rationalize in that situation or in the heat of the moment...