Yep, you need to take her to the vet to check that tooth out.
You didn't say how old your Yorkie is but of course they have baby teeth and they lose them just like humans. Many Yorkie's have dental problems and it is important to stay on top of issues with their teeth/gums. Bad teeth/gums can slowly poison their system and many times you won't even know it is going on.
So, to be on the safe side I would have your vet look at her teeth.
