Greetings, is it pretty consistent that she's good for a few days after the bed is clean.... then pees? If so why not get a second bed and then swap beds... maybe every other night, or even every night. Have one in use while the other is being washed - hopefully thats an easy thing to do or maybe get some kind of top layer thats washed instead of a whole bed? Its certainly worth a try and worst case scenario - you have spare bedding for your cats.

I read a couple of good cat books recently - "Cat Sense" by Bradshaw and one by Pam Johnson. What I got out of them was just realizing how from the cats frame of reference, they generally have a reason for doing what they do.... but from the humans point of view it may make no sense. Also what they emphasized was there can be considerable tension between cats that might not look like the full fledged screaming cat fight, but still be stressful for both participants. Are you seeing any signs of tension, like lashing tails, one swiping or touching the other with a paw, hair standing on end, is one cat maybe "guarding" resources like blocking access to the water dish or litter box? This latter can be cause of cat avoiding litter box.

Poor girl - I wonder if its something about her own smell that she doesnt like after it builds up for a few days? Cats instinctively will periodically move the location where they sleep for that very reason, because if it smells too much like them it may attract unwanted attention from predators. Does she sleep in the pee-soaked bed then or find another spot?

Do you have 2 litter boxes near each other? I would move 'her' box closer to where her bed is and see if that help.

She could be threatened by the location of the litter box if it's near the other cat's box.

Not sure what tests your vet might have done already...do they recommend any additional testing (bloodwork, urinalysis, urine culture, ultrasound or radiographs to look for things like stones)? Do they think it's feline interstitial cystitis? Or? If they've done all those diagnostics, here are some suggestions....

I'd have at least three litterboxes for two cats. Try big boxes (think large rubbermaid containers with a U cut in the side so they can get in easily, uncovered), clumping litter (try Dr. Elsey's cat attract litter, you can get it delivered from amazon or chewey, etc.), no liner, placed in quiet places (not near the dryer or something). I would personally try two litterboxes per floor. Clean them twice daily, as cats prefer their boxes to be very clean. Every couple of weeks, scrub the boxes out with soap and water. If they get grungy, just throw them out and get new boxes. Get more cat trees and beds to reduce stress (cats like to be up high, so make sure they can get up high), give separate food and watering stations. Cat fountains encourage drinking, which can help with certain conditions such as feline interstitial cystitis (I like thirsty cat fountains, available online and on etsy). Feliway diffusers can help with stress. Try placing a small washable bedpad (or disposable kennel pad) in kitty's bed and cover with a comfy, washable, thin blanket, so you don't have to wash the whole bed if there's an accident. Kitty may have decided she prefers to urinate on that sort of surface. If that's what she wants...try using disposable kennel pads in a litterbox. I have a friend whose kitty insists on this setup. But, I suspect that something is happening every few days to make the litterbox a less desirable place, leading to the urinating in her bed. Is the other kitty ambushing her in the litterbox, maybe? Definitely clean every box twice daily.

I have found that the product Feliway helps very much with cat issues. It's cat appeasment pheromone, and I think the best way to use it is through the diffusers. I had luck with it. It seems to damp down their insecurities and certainly helped with cats that didn't like one another.

. . !