Bemybebe.. I don't know the OP, she mentioned her DD's popularity in a later post. Who knows what makes somebody popular or not? It's neither here nor there in terms of worthiness, but it seems to make a difference in the way (mostly) girls treat each other.
I've already said (earlier in the thread), what I would do if I got wind of my daughter treating others in a spiteful way. In my experience, some - not all - but certainly some mothers feel very proud to hear that their daughters are either in or leading the 'in crowd'. It flatters their own egos and blinds them to the realisation that being a bitch is nothing to feel special about. The same applies to some dads at having a 'real man' for a son, but perhaps not so much and I'd say that boys are just not as bitchy or spiteful as girls can be.
I would be very sad were my daughter to be either bullied or a bully herself. I hope that unlike StayingDavidTennantsGirl's mum, I'd immediately find out what happened and take action as necessary with the involvement of the other parents, but wouldn't call the police, I really don't think it's appropriate, not for this.
If I were the parent of the 'victim', having found out that she participated, I would remove her FB priviledges also. In fact, at her age she wouldn't have them. If more parents would stop their children accessing FB, any cases of actual bullying would be more visible, out in the open, and more easily dealt with by the school and/or parent(s). It would be hard though... it's going against the tide and who wants to do that in this day and age?
I'm at a loss to think what the school is supposed to do either to stem this kind of behaviour. The school has very few powers to punish and none to exclude. A poster earlier in the thread commented on the difficulties. Therefore, it has to be up to the parents to be vigilant and punitive where necessary.
What generally astounds me is that, given the number of us who experienced bullying when we were at school, it hasn't been stamped out. I guess it's the same for our own parents who were either from the 'old school', believing the 'sticks and stones' principle, or who were blissfully unaware. I feel desperately sorry for the children who were bullied and have faced much of their adult years with depression and and inability to move on from those awful times. :(
We really can't speculate on whether there was more to this incident because we only have what the OP has posted. It's an interesting topic though and so appropriate just now.