Well, since I'm the kind of person that's equal parts untrusting and paranoid enough to be on my toes pretty much at all times when I go out, combined with having an ethical side that can be best explained by "is paranoid of everyone but doesn't not interact with them, and if they get his ire is nondiscriminatory," I would probably react pretty quickly (assuming the punch didn't send me reeling back) with a quick, theoretically incapacitating punch to, say, the throat (airway damage would probably at least cause some choking) before I had even registered what happened, and then would either A: get the attention of nearby authorities, or B: if there are no authorities nearby, bolt for it.
Not sure if I would get away with it, given the double-edged sword that is retaliation; but I'd like to think I would, especially since I didn't, say, punch her in the face.
Then again, I'm also the kind of person that generally doesn't have a very quick reaction time, but when I do, it's quick; so I might actually dodge it and evade further aggression/pursuit, and just not leave the house for a while. Especially since, living in America, in South Carolina, I have the Castle Doctrine (AKA "Stand Your Ground") to dictate I can beat them into a pulp first and ask questions later if anyone breaks into my house.