My boy's hair on his head is REALLY thin as well. I wondered if he had mites or something before I got him...
What hair he does have is an ok length for his age, but he looks like a balding old man sometimes, especially near his ears. Perhaps our babies just have genetically bad hair? I hope tings improve with your girl's hair, perhaps the suggested fish oil stuff will work. She is completely beautiful, thick floor length hair or not. I guess with yorkies as with people some have model like hair some (like me) do not.