When I was a little girl that happened to me too.But what you need to do is get her going to the gudince consler at her school it worked for me so maby it could work with you also get her to try to be nice to them even if they arent nice to her

say her if she has done a mistake say sorry and say her to ask her friends that what is the problem

Maybe get her involved in some activities where she can meet new friends, or try to get her to go out and meet new girls, you should probably talk to her about why she thinks they have done this, maybe your daughter isnt comfortable with what they may be into now, it could be a blessing in disguise, I would tell her that if that is how they are going to treat her then she dont need those types of friends anyways because those are not real friends and sooner or later the same thing or something similar will happen to one of them and they will know how it feels but there are other girls out there who would be happy to be friends with her.

Hello,
I would take her shopping and get a makeover. Sometimes getting out of the house for a day is the best thing. Another thing would be to find out "why" they have turned against her. Talking to her about solutions is very important right now. Also, there is no problem too big that you can't laugh at it. Try some humor! In times of stress, people need humor!  Let her know that no matter who decides not to be her friend that YOU will always be there for her. Family comes first and all others will come and go. Remind her of who she is and how very special she is.