The first thing I would do is use an enyzme cleaner for the sheets and bedding.You can buy it at pet supply stores, it breaks down teh proteins in the pee. Cats have such a strong sense of smell that sometimes normal cleaners don’t get rid of their scent enough.
Second I would also check to see if kitty has a UTI. That is usually the most common cause for out of the box peeing
Many TDKers also swear by a product called Kitten or Cat Attract. You sprinkle it in their litterboxes, it often seems to help. (Also click the pink tag ‘litter box’ for previous advice on this subject.)