I thought I was going to have some advice but after reading your post, Belle's situation sounds more complicated.

What I have found helps with my Hannah (who does the submissive urination despite the fact that she is an alpha dog) is for people to ignore her when they first come in and not to make too much of a deal over her. Also when we know we are going to have people coming over to make sure she has had an opportunity to "go potty" before visitors come. I have asked my husband to only pet her when she is on a cleanable curface, i.e. kitchen floor or tile entry or when outside. Hannah was raised from a pup and has never been mistreated. She is five years old and it's a trait that we've been able to mitigate by the above tactics but not eliminate.