Should I deworm an IBD/CRF cat (high eosinophils)

My cat has CRF and stomach/bowel issues. She's had a couple blood tests where her level of eosinophils are high, the vet suggested possibly deworming her but said it could also be from food allergies and didn't sound very convinced she should be dewormed. (It was like "maybe deworming would help.")

Her previous vet checked a stool sample a couple weeks before the blood test for parasites and said they didn't see any. (I don't know what parasites exactly she checked for, she mentioned giardia specifically but I don't know if they looked for more.)

Her bowel issues are, she'll have nice normal poop for a while. Occasionally there will be a thick streak of blood on the outside of one of the pieces. I notice that maybe once or twice a week. Then she'll get diarrhea for a little while. Sometimes she vomits. The vomiting was every day a couple months ago, then no vomit until this morning. She went almost three weeks without diarrhea and started back up a couple days ago.

I recently switched her off a fish based dry food (that she was eating almost exclusively for the past two years) onto a chicken based canned food for sensitive stomachs (Kattovit Sensitive). She's been off the dry food for a little more than two weeks and still having the stomach/bowel symptoms.

So what I'm wondering is, should a CRF (IRIS stage 2) cat be dewormed "just in case because maybe it'll help" without a confirmed diagnosis of worms? I don't want to add anything that would exacerbate her CRF. Or should I wait longer to see if the diet change helped?

The only medications she's been on are a dexamethasone shot about two weeks ago. Maybe the diarrhea and vomiting are starting up now because it's wearing off? She also snuck a bite of my puffed amaranth cereal the day before the diarrhea started. Just plain, dry, puffed amaranth. She was trying to get into the bag like it was catnip! What a weirdo. I think she only got a couple little grains, maybe a quarter of a teaspoonful, but maybe that's also part of it.

Since seeing the vet I've also taken away her cat grass and tried to brush her more often (she attacks the brush) because he said the grass and hair could be irritating her bowels further. (This was after breaking open the stool sample I brought in and seeing a lot of hair and a couple grass strands in it.)

Not having experience with a CRF cat, I can't really advise you as to deworming, but having a cat with IBD and food allergies, I can recommend a brand of food that might be better than the Kattovit: Vet Concept, which is a single protein food, with most of the varieties being completely grain-free. They have non-prescription and prescription food, both canned and dry. Some vets carry it or would order it for you, or you could order direct from the website. Since they have a lot of unique proteins like kangaroo, goat, horse, etc., it's very good for elimination diets, which you should discuss with your vet. I've had very good experience with it, as has the shelter where I volunteer.

Do you know if the phosphorous content of the Vet Concept foods is published anywhere? I couldn't find it on their site and when I tried emailing they told me to call. (And I don't have the minutes on my phone for a tortuous phone call in bad German.)

I don't think deworming would be harmful in this case. It's generally safe and can be helpful. GI parasites are often not found in stool samples because the parasite hasn't always shed segments/eggs in the sample you collect. Ask your vet which parasite they're most concerned about and make sure you get the proper deworming medicine. There are some that just do rounds, others do tapes, albon does giardia while panacur covers many of these.