The only reason that would justify striking a woman would be a legit threat to life. A woman smacking, spitting, cussing, nagging, punching eye etc is never an excuse. If leaving is an option do so, if you're confined to an elevator protect your vitals and flee. If she's got a gun, knife, bat etc etc by all means.

If it's a dude doing those things, drop you cell phone and do it.