How to get my cat to stop peeing on carpet and blanket?

She uses both her litter boxes and she's the only cat too. She LOVES to pee on my son's comforter and the stair landings. I don't know why! I bought the pretty kitty litter and her pee is normal. Her other litter box has worlds best cat litter. I'm at my wits end! She's 6 months old, we got her 4 months and and has been doing this for at least three months now.

I'm in USA, I'm not a minor, she has a vet and had a normal checkup, she's spayed.