Hair problem

[Austin.Texlee]

Hi all, I'm Austin and I'm new to this site but I've had a German shepherd for three years now.
Anyway here's a little background info and the problem she is having. I got Her 3 years ago from the local shelter and she has been my faithful companion ever since. Back in October right before a hunting trip I noticed her scratching and biting her hindquarters a little more then usual. I just figured she had an itch, a week into the hunting trip my mom brought her up with her to stay the last couple days and I saw that she had knawed a spot about 4 inches across on her backside and it was all inflamed and covered in puss. We took her to the vet and he said it was hot spots and shaved around the area and treated it and told us that it was from an allergic reaction to something in the air during fall. It's all healed now but her hair won't grow back, except for directly over the spot, everywhere else is bair skin with "peach fuzz" on it. Do any of you have a recommendation as to what to do or what could be causing this?
-Austin