Thank you all for the suggestions. Actually the kitty litter is the first thing I thought of, so I have tried every brand out there including just plain dirt from the garden. She actually has a bad habit of running down to the litter box, pooping on the floor and digging the litter out to cover it. (drives me nutz).

She is on a medication called Clomipramine. It makes her sleep, but as soon as she wakes up she starts to wash again.

I think I will try a new vet. He has been looking after my animals for 10 years, but at this stage I will try anything. At the moment I have resorted to putting her into a light cotton baby sleeper just to stop her from licking. So far she has licked two holes in it.
Keep the suggestions coming. I am desperate.