I don't think there's a perfect answer to this question.  In my experience from just a couple of years ago when my daughter was that age, ten year-old girls (and boys) can be pretty mean and nasty, especially towards someone who is a little different (my daughter has flame red hair).  Our approach was to do what we could to reinforce with her that she's a wonderful person and that her best response would be no response and especially to stay calm.  We persisted with her and were, after a time, able to find one or two girls that she could become good pals with.  Though it wasn't the case with us, it might help to find other girls that do not go to her school.

I'm not sure if I can help you, but I will try. Self-esteem is an important issue at really any age. However, I would make time for your daughter when she is out of the school environment. Maybe take her to get some new clothes, do hair, make-up, etc. So many kids are now looking to other kids for approval. What we need to be doing is teaching our kids that they are special without these "approvals" and being independent is a good thing. However, this is hard to do once a child has experienced that type of rejection. The hurt can really damage the child's trust. Since we homeschool, we have not had this issue yet. All the kids play together and the "friends" are not so defined. There are no cliques and everyone is accepted. I would just talk to her and help her to make choices about who she hangs out with. Good Luck! This is the trouble with and a prime example of negative school socialization.