We just had the same problem with our cat before we moved. He started peeing on our bed when we had a house full of guests visiting and they would lock him out of the room his litter box was in. So, we moved his litter box to a location he wouldn't be locked out. Unfortunatelly, it continued to happen after everyone left. Only this time he would pee near one wall in the dining room. I then started to reflect on similar issues I've had with other cats I've owned in the past. It couldn't be a bladdar problem because he had no blood in his urin. So, it had to be teritorial because in the five years we've had him he never did this until the neighbors next door in our apartment complex got a dog. He must be peeing on the other side of the dining room wall and my cat could smell it. Our cat stopped this behavior once we moved.
Before we moved we had to clean it up and get the smell out. My husband went to Pesmart and they refered him to a cleaning product that worked well and then we sprayed Febreeze to help with the smell. I know there is also a product out there that you can spray in areas that will deter a cat from peeing there.
My suggestion for you would be to first check with your vet and make sure your cat doesn't have a health reason she is trying to tell you about. If they determine it's behavioral then they should be able to advise you of methods to correct it. I know cats can get very jelouse and very teritorial. Sometimes their behavior is a way to communicate what is going on.