Gary, that sounds like you are doing just what Princess needs for you to do. Having her checked out by the vet is an excellent idea.

My Senior girl Peony sometimes leaks on the couch... even though I have a litter box on the floor right next to the couch with a little stairway from the couch to the box, and another one ON the couch in case she doesn't feel like going downstairs. Then there's a cat bed for her in the middle of the couch and then there's the spot where I sit next to the lamp. Sometimes she just pees on the cat bed if she doesn't feel like stepping into the couch litterbox.

I put plastic sheets of one kind or another on the couch.. shower curtain liners from the dollar store are my favorites.. and towels on top of those. Much easier to toss the towels in the laundry and wipe any leakage off the plastic covers than to try and get out pee spots in the couch cushions.