My only advice would be is make sure the vet clears your pup from any sickness that could be making him not eat.
After you do that & tests come back clear I'd try to find a good food that your yorkie enjoys & know when they get hungry they will eat! Don't continue to buy new food because you will just create a very picky eater so find something that she likes even a little bit and just stick with it! IF she's had any shots, or heart worm medicine that could have something to do with her not wanting to eat. Give her sometime! Also make sure you are not giving her too many treats because they do have small tummies and too many treats will fill her up quickly. Good luck!