My grandaughters 6month old female kitten wees in chairs , on cushions , on the bed, and anywhere else she can. She was very good when they first got her and used the litter tray all the time. She does go out but doesn't like it. They also have a male neutered tom.
Cats can be really fussy about how clean their litter tray is. My two cats (one female, one male, both 4 and a 1/2) go out but I still keep their tray in case they want to use it, but they are fussy about using it when it's not almost perfectly clean. I make sure I have a full litter replacement and detergent spray on a regular basis. Then I get problems if they haven't been outside! They can also be fussy about how much litter there is in the tray.
we have a female cat she is about 10 now. she pees everywhere too, and also is an indoor cat. we have never found what the problem is, she has a clean litter tray, a cat flap she can use. she is a shy timid cat and i think it is when she is nervous she pees.
jrobinson I've had one of those too! Never did work out what the problem was. She went through phases. Bought a plug in scent thingy, that worked for a while.
I think I would have her checked out by the vet and ask for advice there. There has been a change in behaviour and something must have triggered it.
All the best.
based on a very recent problem i have had with my cat, i would recommend you take her to the vet too. if the cat has a urine infection and it hurts them to wee, they may associate the pain with the litter tray and start to try and go in other places.