Halo is a premium food but it could be a specific ingredient in the food. I would go to the site
Dog Food Analysis - Reviews of kibble and find the list of ingredients in her current food and keep them as reference. Then find a food with very few ingredients to feed her and see if she reacts to those ingredients. Keep a list of what ingredients she reacts to and does not react to. Then you will be able to use the list to shop for food. Buster gets fleas when he goes out for walks and once they have bitten he will chew/scratch the itch/bite even after the flea is removed. But that does not address her vomiting. I would look through the
Yorkie Health & Diet - YorkieTalk.com Forums - Yorkshire Terrier Community section. Many YT members pups had the same issues so they could provide a lot of first hand knowledge on food allergies. I hope Bella feels better soon!