If she was acting alone, then no direct witnesses to lie for her, so I'd punch her right back in the abdomen, then make a scene asking her why the hell she hit me before she can even get a word out, at the same time, I'd feel my own face to get the message across that I got hit.
If she was in a group, and they were watching her, I'd make a scene, asking her what the fuck was her problem, making it clear she was a stranger. If repeated punches, there would be a crowd watching and it would be clear she's a fucking psycho and I could sock her in the throat.
That would stop her instantly.
Yes, if you attack me, I'm going to make it my goal to knock you out, and look as innocent as possible doing so.