Hi there Benita,
Wow, you've taken her to the vet and they haven't been able to suggest anything to help, that's too bad. I'm not a vet, but there are some probiotic supplements that will help to increase your cat's gastrointestinal health that you can try, it could help. These two products come to mind: Probiocin Oral Pet Gel, it's a probiotic and easy to give small animals, as well as Feline Fortiflora. Good luck, if you don't see improvement, back to the vet is best. Also, make sure to watch for signs of dehydration and provide your cat with lots of fresh drinking water.