Sometimes we forget what we are doing to our own children. We think they can understand children who bully, they don't know what there problem. Children find it very strange when a child open his mouth and all that come out are bad words.
Now these words might make your child feel sad and make them feel I don't belong around these children who talk with these bad words. Bullying comes from a child who has problems with words...only words are words. Be nice! It doesn't take a lot of words.

Have you considered homeschooling her? It's not a viable option for every family, but sometimes it can work. One of my daughters was bullied at school and had very low self esteem. We started homeschooling her in 7th grade. She did so much better once we made that decision.