I agree with Dionythicus about the girls parents needing to have been more proactive, but that is just the beginning. I think they should have been at the school "shaking trees" until a solution was found, if the school wouldn't help them they should have gone to the district, the news, the police, social services and anyone else they could get a hold of. All in addition to getting the girl some professional help for her own well being. Remember the squeaky wheel gets the grease.
I also think that if you are going to require that kids attend school (and kids do need an education), then it is the schools job to also be proactive about keeping the kids safe. If the issue had been brought to the schools attention, then why were these kids still allowed to interact with her, once the problem became severe and chronic why wasn't the school trying to keep those kids away from her? Change up their schedules and put them in different classes, or send them to in school suspension, or monitor them in the hallways and at lunch.
And most of all what about the parents of the bully kids? I know that you cannot control everything your kids do, but I can assure you that if one of my kids was a bully, first they would be punished and spoken with about our families values regarding respecting people, but if that didn't help then I would do whatever it took to make that lesson crystal clear. If that meant that I had to attend school with them everyday and walk them from class to class to make sure that they were not torturing other people then that is what I would do. If they were posting mean things on other people's facebook page then my kids would not have the internet anymore. Being a parent is hard and you cannot control everything BUT it is important that you work really hard and that you and your family is a model of respect and kindness. Not every lesson that a parent tries to teach is going to be internalized, however I personally believe that being respectful to people and really to life in general should be a cornerstone of a families values and that all other rules come from there. Parents need to model respectful/kind behavior and they need to talk with their kids about how important it is and they need to be clear that treating people unkindly is not acceptable. At my house you are either respectful to all people or you have your Mom and Dad to answer to and I can assure you that if you are in a position to have to answer to me or my husband it will not be fun.
However I do not agree at all with tyflier (sorry nothing personal - and this is just an opinion so take it only as that) I do not think it is ok for kids to be mean. I don't care what kids might try to get away with. It is IMPORTANT that their parents, teachers and society in general do not just brush this off. Being mean is not ok and should not be considered acceptable behavior. Adults, especially parents and teachers should be models of appropriate behavior. And they do have a responsibility to address these kinds of issues.
The kind of people we raise our kids to be effects our society and our future, and if we tell kids through our example/actions/lack of actions that being mean and nasty will be overlooked and allowed then what does that say about the kind of society/future we will have. If we tell kids that it is ok to be cruel so long as you don't touch the person, then in the future you will have women and men who are verbally and emotionally abused as adults who accept it because the abuser didn't touch them. You will have abusers who think that so long as they don't touch you anything else they might do is fine. And society will be conditioned to ignore a persons suffering because after all they are not actually being touched so it is no big deal. In short allowing kids to torture other kids is just going to lead to a generation where being a sociopath is considered normal so long as you didn't physically hurt the other person
Everyone involved could have done more, and it is to be honest completely inexcusable (in my personal opinion) that they did not. Her parents needed to get her help a long time ago, the school cannot force kids to attend and then not properly supervise them while they are there, and the parents of bullies need to be involved to put a stop to this on their end.
The bottom line is that being a parent and raising kids is a HUGE job and it is a very important one. Either be prepared to do a good job, or don't have kids. I am so tired of people who have kids and then SLACK when it comes to raising them.