I am currently having the SAME problem at my house! I have 2 females that HATE eachother. They are both spayed as well, and one pees where the other likes to sleep. And guess where that may be? MY BED!!! i have changed the sheets 5 times in the last two weeks and it is getting annoying. I have taken to closing my bedroom door and generally keeping her out of there comppletely. If it is possiable for you to do so...i would put a litter box on or near where she is peeing. That might make her want to use it. You can also try keeping the peeing one away from these areas As Much As Possiable. I know that this can be hard to do...but so far i have not come up with anything else that is helping!