Your dog is gorgeous btw!
Just for reference, my 9 year old is about 4.5lbs. Perfectly healthy.
What I judge her weight by is this.
Feel her rib cage, and trace your hand back towards her butt. If her stomach/gut extends past the rib cage as far as size, she might need to drop a bit of weight.
I hope to be corrected if I am wrong, but from what I have seen from my experience with these dogs for the last 12+ years, if the gut is even to the rib cage you have a very healthy yorkie.
If you feel your way backwards and the gut is wider than the rib cage, you might want to cut down the food a bit. Or, if opposite and the back end is skinnier than the rib cage, you might want to up the feeding.
My girl's back end (from the rib cage back) is even with the rib cage and the vet said she was in perfect condition.
