Sounds like it could be a slippery slope on what constitutes harassment, but I empathize with women who get unwanted attention. They should not have to put up with it. The classic response would be for a woman to slap the face of the offender, but I think that only works in the movies.
She could hit him with her baguette?
Or maybe they could grown up and not care about whistling instead of stamping out free speech.