I had that problem with my female Kira when she was a puppy. Her vulva area is deformed somewhat and she got several infections so she was on antibiotics a lot. I took her to the vet and she told me that because her body was under stress from the medication her immune system was not 100%. It is hereditary mange. It is not contagious but it can kill them if left untreated. The vet will do a simple skin scrapping and look at it under the microscope. There will be mites in it. It is no big deal really but she should not be bread because she will pass it on to her puppies. It is very common in all breeds with coats like this. I have even had a boxer that had the same problem. Changing the food could help too but most likely you will have to get a topical creme from the vet and put it on the area and within a few days the hair will grow back. You will most likely notice this when they are stressed. Both my Pits have skin allergies as well lucky me. It comes from poor breeding aswell. Hope this helps.