Yes, as others have already mentioned, please take your cat to the vet for a check up. She may have a urinary tract infection. My oldest cat who is 11 years old also just started peeing outside of the litterboxes. I had him checked out and he's fine. He's just been very grumpy towards his siblings lately so I bought some feliway plugins to help calm everyone down. It's working some what.

I live in a condo and I already had 5 litterboxes but I added 3 more. I put 2 where 2 of my cats started peeing and I also bought some cat attract litter which you can buy at Petsmart. I put it on top of the old litter in all of my litterboxes and now they're using most of them again. I also cleaned up my older litterboxes very well with soap and water. So far it's worked well with my gang.