Here are a few things first off it could be a medical problem you should take her to the vet and have them run some tests and I agree take some poo with you (he he that rhymes) but seriously have her checked>
The other thing is if shes a long haired cat it could be sticking to her. Do you have a covered litter box or is it near her food or water? cats don't seem to like having there litter box near their food or water their picky that way.
Have you change the litter brand? we switched to a cheaper brand and our cat didn't like it very much so we switched back to the old brand which works for her.
Natures miracle works great best on the market as far as I am concerned.
Hope some of this helps
