Witholding food for a while is a good suggestion, it allows the stomach to calm down. I'd also recommend keeping an eye on the litterbox to make sure that nothing weird is going on there. For example, if she also has diarrhea she could get a little dehydrated, but if she's having trouble making poops it could be a whole other set of issues. Also, keep an eye on her behavior. Is she lethargic or acting funny in any other way? Also, is she acting as if she's in pain in any way? Head down, pacing, hunched? If the answer to any of those is yes, I'd recommend a call to the vet right away.
Mom to 2 crazy kitties and 1 African Clawed frog.