When in “no go zones” in NYC, it is probably best to keep lessons in etiquette and courtesy to yourself.
As I've stated a couple times above, I agree that she shouldn't have said anything to that little p*ssy that might have been taken as even slightly offensive. Now if she were built like the brave and decent guy who came to her aid it would be a completely different story.
In any case, I would advise her in the future to simply get the hell up and move to a different part of the car if some creep spread his legs wide apart while sitting next to her in one of those small 2-person bench seats at the end of subway cars.