Strangly enough, I have just posted about this, under the Insurance thread.

Our George had this shortly after we adopted him. We were told he might have kidney problems etc but it wasn't it was idiopathic cystitis. The vets think the stress of moving to his new home might have trigged it.

He stayed over at the vets for a couple of weekends and we had a couple of pills to feed him daily (that was fun) but it cleared up.

We had to swap his diet from dry food to wet (which he loves) to make sure he got enough water. As soon as he wasn't in pain, he had no problem with his litter tray.

We also had him on an anti-depressant pill.

Some vets think that this helps the bladder mend. Although in our case, one vet told us to feed George the Anti-depressant pills and the next vet (same practice) said 'stupid modern ideas' and said not to give him the pills. Make your mind up !!!

Don't worry she'll be back to her normal self soon. As soon as she can pee painfree, she'll be using her box again.

Keep us updated, all the best.