If my suggestions are tried but are not successful, you should meet with the teacher and principal and explore other options. Depending on the situation, you may want to transfer your daughter to another class or you may want to take her for outside counseling in order to help her build greater self-esteem. This will help her handle social situations more productively.
Do all you can to protect your daughter and to strengthen her self-worth and resilience. Your daughter needs to feel safe, while at the same time you need to ensure that she knows how to handle herself in all types of situations. Hatzlachah!