Why is my dog suddenly licking her bottom raw?

My 1-1/2 year old female maltese started licking her back end after being groomed yesterday. She was spayed at age 8 mos. I don't know if she was doing it yesterday after we got her back home, but she is non-stop licking it today. The area around her is bright pink and swollen. Her rectum is actually dilated - the opening is enlarged. There is no bleeding. There is no discharge. They did shave around that area to make it cleaner for her after eliminating. I noticed that when she isn't licking herself, she likes to sit on the cool tile kitchen floor, which I'm uming the cool tile makes it feel better. Could this be a fungal infection she picked up from the groomer? Can I use a monistat type cream on her to help it? I have an appointment with her vet for Tuesday. She is not whining or crying or whimpering. I don't know if I should put a shield thing on her or not. I don't want this to spread if its a contact dermatitis or fungal infection as I plan to go out of town next week and place her in a kennel while I'm gone.