Sounds like she might have mites or also called mange. It is contagious for other pets and humans. They are tiny bugs only seen under a microscope and they burrow into your skin and lay eggs itchy very itchy. It can be treated see a vet.
My Dog Is Biting And Licking And Pulling Her Hair Out Of Her Right Hip. She Has Chewed Away Her Hair. Can Anyone Tell Me What Is Wrong With Her?
She could have a rash, or a thorn. But really the best thing to do would be to take her to the vet. Good luck.