The only answer I have is to take her out more often?????
I wonder, though, if it isn't just her age. Who knows? Yorkies can sometimes be so bratty and at other times be so sweet.
Maybe next time you find a spot go get the cleaner and try lecturing her while you are cleaning it up. Let her see that you have to clean it up.
None of mine (knock on wood) have ever been biters except when they were little puppies biting at me. After they left their puppyhood, they never bit at all.