Well, I am assuming that removing her from that situation and homeschooling isn't an option or you would have considered it. The world inside a school building is so unlike the real world, where if what you describe happened anywhere else (job, grocery line, etc.), it would have been taken care of easily. My only advice is to be there to let her vent and have your shoulder available to cry on, because I don't believe there's much else you can do without the other parents and the school admitting that these other girls are doing anything wrong.
Will she learn from this? I can't imagine what could possibly be learned from it. As I said, if an adult is bullied, they have the option to remove themselves from the situation and if it gets physical, an adult has the option of calling the police. Your daughter has neither option while she is enrolled at the school. I wish you both the best.