Do you think it is possible she is a little bit incontinent - this can happen after bitches are spayed. I had similar concerns with Betty - every so often she would wee on one of the beds - fortunately it was never much and only got as far as the quilts which were promptly dumped. Betty turned one last week and we still get the very odd little accident out of the blue. She could also have a urinary infection - you may want to take her to vet to get her checked out and ask for advice.