Rabbits usually have less hair in that area in general.It could be urine scald, where she may be getting some urine on her skin. This causes irritation and secondary infection in some cases.If the area appears moist ever, baby powder can be applied in small amounts to help absorb the urine. Softer feces that get stuck to the area may be the culprit, but the skin irritation would be seen once the fecal material was removed. Other rabbits may get external parasites, such as fleas, mites, or lice. Usually there is more generalized hair loss, especially on the ears, and often they are itchy. Lastly, some rabbits get rectal polyps or papillomas. These would be the fleshy swellings I referred to earlier. They look like multiple, cauliflower like masses that protrude from the anus. Definately check the area daily, keep her and her enclosure as clean as possible, and use baby powder if the area is moist. If it continues to get worse, or it looks like the description of papillomas, have her checked out by a vet that regularly sees rabbits. Let me know if you have more questions!
Dr. Chenoa