You really should take her to a vet. Is it symmetrical or patchy? Is she biting at her fur at all?
When our puppy was itching/scratching a lot, the vet initially thought it was puppy dander. A month and a half later, his fur was super patchy and he looked naked across his belly and legs. After doing 3 scrapings at the vet, we found out he had mange (a mite). There are two types and the only way to cure your dog is through either dips and ointment (mite #1) or a product similar to Frontline (mite #2). Our puppy had mite #1 and has gone through 3 dips now, and while he's not perfect, he looks MUCH better.
I'm not saying your dog has mites but, if she does, you want to help her.