I've got to sit this girl down because she needs an ally, she needs support and she needs to learn how to handle this in her lifetime.
We all run into bullies sooner or later in adult life (in-laws, employers, rude people) and we need to be able to assert ourselves successfully and stand up.
You need to go online and Google "ASSERTIVENESS SKILLS" for her to research, read about and learn the exercises.
Meanwhile, you need to get the names of the bullies and the details of the incidents and make an appointment to see her school principal in person. Your desire is to have your child feel safe at school and become successful. This is why you are bringing this to the attention of the school principal and you're expecting action.
You don't have to tell your child that you have spoken to the principal. Encourage her to stand up for herself so that she can succeed in life.
As Eleanor Roosevelt said, "That which does not kill us makes us stronger." She needs to grow in strength and purpose.