My cat is breathing fast and not peeing after IV fluids. Is she okay?

If your cat is breathing with an increased respiratory effort while on IV fluids, she is likely accumulating extra fluid in her lungs. Not urinating for 5 hours while on IV fluids is not always a reason for concern depending on the level of dehydration at the start of fluid therapy. Since your cat is receiving fluids intravenously through an intravenous catheter, I assume that she is being hospitalized in a veterinary hospital. Her vet should be able to examine her and determine if her fluid rate needs to be decreased and if she needs to receive diuretics if she is fluid overloaded. If for some reason she is not in a hospital setting, she needs to be taken to an ER immediately.