I think you should talk to the librarian for starters. Give her examples of your daughters reading level. Ask if she may check out different books? Tell her how it would effect your daughter in a positive way.

I don't think your daughter should hide her abilities.

I would have a talk with the teacher. What she can do to challenge your child? If that doesn't work talk to the principal.

How do you know she is HG? Did you have some testing? If so show results to the principal.

I would look around to see if there are other school options or homeschooling even if you are not ready to make a move yet. This gives you time to learn.