You might want to take her to the vet ASAP!! Is she a puppy? If so it could be parvo. It sounds like it. Both Buster and CoCo and got Parvo when they were puppies and we took them offhand because we know how dangerous Parvo is. It doesn't take long for Parvo to kill a dog. I have had a few dogs that weren't so lucky when the parvo disease. Please consider taking her to the vet.