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Sometimes when a dog has diarrhea, the anal sacs that are present on either side of the anus can become full and painful (the firm feces helps express the contents of the anal sacs, so with diarrhea, they can get very full). This may be why she is licking her anus raw. I would go to a pet store and purchase an e-collar (cone collar) for her to wear so that she can't lick her anus. That is the first step, because otherwise it will continue to get worse. Then, for the diarrhea, I would try feeding her boiled chicken breast mixed with white rice in a 50/50 mixture for the next week, and then once the diarrhea stops, wean her back onto her regular food slowly. I would also try giving 1 tablespoon of canned pumpkin twice daily, as this is a natural fiber that can help with the diarrhea. Then get her in to a vet to get her anal sacs expressed, and that should help. If the diarrhea does not resolve, it is possible she could have intestinal parasites causing all this, so you should take a stool sample in to your vet.
Best of luck.