The most common parasites for we humans to get would be intestinal parasites, especially if we were to pick them up from a pet. If her kitten was never diagnosed with parasites and has always been healthy, this would seem an unlikely source. The symptoms of an intestinal parasite infection would be diarrhea, mucous in stools, abdomial cramps and gas, distended abdomen, perhaps fever and fatigue. I realize she has pain and vomiting from the gastroparesis and may even have a distended abdomen. A stool sample can easily be tested for parasites.

Other parasite infections could be in the blood, lungs or cerebral spinal fluid. All these can be eaily tested for. Of course the test for blood or lungs is much easier and less invasive that the spinal tap required to test the cerebral spinal fluid. Here is a web site with a comprehensive list of parasitic diseases: Parasites & Health

It would be impossible to diagnoses a parasitic disease without a test unless the parasite was visible in her stool, of course.

She probably has been told many times about treatment for gastroparesis but just in case she would like more information please see this web site: Gastroparesis: Treatment

And another website for a 3 step diet program to manage gastroparesis: Gastroparesis Diet for Delayed Stomach Emptying

It sounds like her immune system is really weak with all that she has going on. Has there been any other diseases considered as the cause of her gastroparesis since she had that well before the diabetes?