To be fair, I doubt any of us really know what was said about her. I doubt very much that it ended with things like, she's ugly or she needs a bag over the head. I'm certain it was much worse then that.
Has she opened herself up to that by being a cheerleader? I suppose she has but that doesn't make it right and it certainly doesn't excuse public forums, such as team sites or Facebook from allowing it to happen. Even we, on this site, have rules against such things and we are much smaller then either of those. No excuse for allowing the content IMO.