Really bad breath can indicate a systemic problem or more likely, bacteria growing and clinging to dental plaque under the gumline. A vet visit for a check of her gums and teeth should be able to tell you if she's in need of a professional dental cleaning, where the vet scrapes under the edge of the gumline and cleans the teeth of dental plaque and beginning dark spots which can turn into caries. I had a dog once who had bad breath and before long had blood on his muzzle. Turns out he had a tooth that had abscessed through his upper lip that had to be pulled. After that, it was bi-annual visits to the vet for dental checks, tooth brushing and yearly cleanings by a professional. Bad breath was gone after the professional cleaning.
If you don't get a vet to check her teeth and gums and she is forming caries and pus pockets and worse, she could wind up in a lot of pain from infection/abscess, losing teeth and the ability to eat and defend herself normally.
Many Yorkies are genetically predisposed to poor dental health and if you will Google the phrase "Yorkie dental problems" and Google Image the same, you will see examples of what a Yorkie's gums and teeth can get into without proper care.
https://www.google.com/webhp?sourcei...tal%20problems https://www.google.com/search?q=York...YQ_AUoAQ&dpr=1