Firstly, no one has the right to put there hands on someone else.
Secondly, You shouldn't have hit her, in that situation, push her to the ground if she gets up and starts punching you again, well then you don't really have any options other than to fight her off but don't fight like you would a man, just use enough force to stop her, it sounds like she was being pretty violent, punching her should not really be an option unless nothing else works, remember if you punch a man you might give him a bruise, punch a woman and you could break her jaw.
There is a difference between abuse and self defence but some men when a women hits them take the opportunity to smack them as hard as they can, hitting a woman for a man should be the very last resort but should not be condemned if it his only option to stop himself from being attacked.
It is about knowing when to use force in self defence and how much to use, most women will stop if just pushed to the ground, remember.
Most people associate it with a sexes thing but the bare bones of it is weak vs strong, an adult should never hit a child, a younger person should never hit someone elderly, no one should ever hit someone disabled and man should never hit a woman, its cowardly but as I said there are exceptions in the extreme just remember hitting should be a last resort in any encounter.
