Bad cat

Any of you out there know how to cure a cat from peeing where it isn't supposed to, especially since there is a litter box that is cleaned out every day?  My cat peed on my bed for the third time early this morning.  Nothing like rolling over and getting a wet foot.  I have no idea why she does it.  The box is only 5-6 feet from the door of my room.  I've had her checked out at the vet and she doesn't have kidney problems and her bladder is fine.  She hadn't done it in a long time so I'm wondering why she did it early this morning.  Looks like I'll be making another appointment with the vet.  It's time for her  yearly check and shots anyway.