Your daughter should not have to miss out on her education because of bullies, however it's understandable that it's causing her to want to stay away out of fear.
I have had exactly this situation with my daughter, I set up a meeting with her her teacher and Head Teacher to decide how to handle it. She was being bullied online (death threats) via school email network, so they were pretty stupid as it was easy to identify them and see proof of what they had said. They also managed to isolate her during breaks, lunch period and when she went to the bathroom. We arranged for her to volunteer in the school library at these times, so she was never alone and could make friends in a safe, supervised environment. After a while she recovered her confidence and was able to move on.
The school is responsible for making sure children are safe while at school, and they should also have written policies about safeguarding and bullying- ask to see these policies and quote them if they don't respond quickly and positively.
Finally, you have to be super-patient, kind and encouraging with her, she might lash out at you or get very withdrawn as an emotional reaction.