How to know if fluid is filling a kittens body cavities?

I asked yesterday and didn't get any good results, so I'll try again.

My kitten may have the wet from of FIP.

I need to know how to tell if her stomach bloating is from the FIP or if it's from worms (she has been dewormed twice, and will be again this thursday). Her abdomen was not barely swollen 2 nights ago, and when I got up yesterday it was twice the size of the rest of her.

What should her abdomen feel like if it is filled with fluids? Squishy, firm, or hard. It is currently firm, kind of like when she had worms, so I'm not sure if I should worry or not.

The vet thinks she may have it, but even the tests are inconclusive. They only can only detect the fact that there is a corona virus present in the body, and this virus may or may not mutate into FIP.

The only way to tell for certain is to do a biopsy of the affected tissue, and that works best in the "dry" form of FIP. My kitten is showing symptoms of the "wet" form.

I've done a lot of research into FIP, as 2 of my older kitties tested positive for the titer, which means, they either carry the corona virus that may mutate into FIP, they have been exposed to the virus and developed antibodies, or they have FIP.

Even if you get a negative result from the test, they may still have it and the body can no longer make the antibodies for it.

See why I asked?