It could mean a few things. One may be worms or the anal glands could be blocked,I also have seen dogs with fleas doing that. Take her to the vet if nothing else.
He doesn't like having poop on his butt hole, don't you wipe after you poop?
I have had Yorkies for many years and It is my understanding and relying on infromation from our groomer, that dogs have these glands on their but that need to be cleaned often. Groomers take care of this by cleaning the Yorkie's but.