I'm trying to communicate to her she is definitely not powerless. I used the example of a cat: Not very big or as powerful as a dog, but you still wouldn't pick it up and mess with it. She doesn't have to be as strong as the bullies, as long as they know she won't tolerate any (physical) abuse.
Teach your daughter she does not need your approval. Teach her to make her own decisions, even if sometimes other people don't like it. Help her figure out how to make good judgement calls in the face of difficult circumstances. Give her opportunities to make real choices and back them even if you do not like them. Let her know you don't like all of her choices but you accept them and respect her right to make them. Do not make her dependent on being liked and approved for everything she does.