After all, we're talking about touchy-feely southern California...I'm surprised they didn't bring in a special counselor for these girls. And knowing how teenage girls are wont to stick up for the underdog and the "oppressed", I'm surprised that at least most of the class didn't stick up for her. You know the sort of things they teach in school nowadays.
And you never know; it could be some liberal but misguided gym teacher who sought to protect this girl from further harrassment and just botched the whole thing up beyond all recognition.
But if you ask me what I would do? If I had been the gym teacher or the principle, and it turns out the other girls were really uncomfortable (we only know that the girl was told that the other girls were uncomfortable), I would have started by sitting down with all the girls in the class, first without, then with, the other girl in the same room, and heard what they had to say about it and got them to talk about it...and then I would have played it by ear depending on how that discussion went down.