it would depend on the situation... if this was a woman you knew/loved/cared about, and she was angry/frustrated/scared/etc at something and had lots of rage and just snapped and needed to let loose and you were the first thing they found to hit, I would have to just try to defend myself.
If, however, I was being intentionally attacked and she was trying to hurt me, I would put a stop to it myself. I'd deck her in the face and knock her ass out.