I will ask the same question I posed to Kitrick. How many times, and how hard, CAN a woman strike a man before he can reasonably retaliate physically?
I suppose that's going to vary from man to man. If that woman isn't armed with a blunt instrument, I'd give her a few attempts to blow her steam off before I wrapped her up to stop the blows. That's if I was trapped in an elevator*. If I was in the open, I'd just walk away (run if necessary) or call attention to her erratic behavior to shame her.
I suppose there is no "right" answer is there? In your hypothetical you feel compelled to allow the woman "a few" whacks while maintaining that it's never ok to strike a woman. However, as "justified" as it may be to allow the woman "several attempts" due to difference in average physical prowess... your opinion is still based on old-fashioned ideas of chivalry and gender roles, not dissimilar to old-fashioned ideas about physically disciplining children.
Still they are your opinions and not universal truths. But you still fail to answer the actual question posed -
Quid pro quo? If I may subsitute the word "fair" for justice for a second... How many punches by a woman does it take before it's "fair" for a man to punch back? A quantitative number is obviously insufficient as an answer, and thus in the absence of an absolute paradigm we only have our legal system to lean on. As such, according to our legal system, a man CAN successful maintain a case of self-defense case against a woman given the right circumstances.
I can perhaps invent an answer to your question of when it's "ok" to hit a woman, but I imagine there are plenty of real life cases you can find on the internet where it's been "justified".