Welcome to YT! I'm so sorry you're having this type of problem with your yorkie! I don't have any knowledge to this type of problem, but I see as to where it would get frustrating for you. The only suggestion I can think of would be to get her some doggie diapers. Here is a site with excellent ones...they are made really well and look cute, and would keep her accidents from flooding the area.
http://queenbk9.smugmug.com/gallery/338279 Here's a couple of pics of my Maddie in diapers from that site. I got her diapers to wear while at other homes so I wouldn't have to worry about an accident.