Hard swollen kidneys

My 6 month old Fluffy cat has 2 hard swollen kidneys. She eats and drinks normally. She does not vomit, urinate abnormally, or have anything else wrong.

She has been to 3 different vets, each twice in the last week. One said it was probably polycistix.

Her kidneys are both swollen and firm, precisely the same size. Google leads me in circles from she's gonna die to just needs antibiotics.

I noticed it a week ago. It seemed to just come on overnight. She didn't seem as playful one morning, I picked her up and while rubbing her tummy felt a knot on each side.

There is nothing she could have gotten into (poison), any ideas what is going on?

Wow!  Sounds very disconcerting.  I wish I could help you, but I have no experience with this.  Good for you for trying to figure out what's going on.  My only suggestion would be to see if you could get her into a vet school teaching program if you have one close by.