Though I feel horrible for Vanessa....
I think that if it were another girl who was being bullied she would support it (not aggressively), but she would be too weak to speak up about it and/or stop it.
Don't get me wrong, because I cried during this movie and wanted bad things to happen to those girls, but I do think that Vanessa was too overpowered by peer pressure.
I do think this movie is realistic. Something similar just happened in Massachusettes - Phoebe Prince dated a popular guy and got bullied so badly that she hung herself to death.