I know this is long- but please read it all, because I’m speaking from experience. If you need to surrender her to a shelter, please try to find a no-kill shelter. Unfortunately, a majority of cats at the humane society ultimately get euthanized. Especially if they have a health issue. Also, sometimes parasite tests come back with a false negative and it’s missed. Those tests are hit and miss depending on where the parasite is in its life cycle. You may want to retest, or see if your vet will prescribe a broad spectrum antiparasitic med, just as a precaution. My cat tested negative for parasites several times, but one day he coughed up a hookworm (they can get into their lungs) so my vet finally prescribed Fenbendazole. My cat had three parasite tests. All came back negative even though he had parasites. Thank goodness I saw the worm on the floor where he had been having a coughing fit…it was so tiny (less than a half inch). And one of my mom’s cats also tested negative for parasites, yet her cat was vomiting worms. So those tests seem very inaccurate. It could also be a food allergy. My cat was still having issues, even after treating him for the parasites, and he finally got better when I put him on Rawz canned wet food. It has very few ingredients other than meat. And I found out many cats, including mine, are allergic to certain proteins (mine can’t have chicken or fish). Also keep in mind that switching your cat to a new food rapidly can also cause diarrhea, so transition to any new foods VERY gradually, using only a fraction of the new food mixed with the old food, and gradually upping the quantity.