If the bitch deserved it, then I don't see any point why she shouldn't get slapped.
In past I had pretty much fucked up relationship with someone that didn't hold his hand back and I've got some bruises back then, at least till the police knocked to our doors, called by my neighbour. That shit is terrible, of course, and should be punished.
But if a woman would attack a man without a reason, then sure, hit her as hard as you can, she deserved it. Unfair because shes weak? God damn, get used to it, it's a hard world. Don't attack someone unless you know you will knock that someone out, otherwise except to be hit back :P