Hi Kim!
Welcome to YT
Wow - that is some trouble you have had with your little one
I am sorry to hear you have had so many problems with it, but unfortunately it is not new for me to hear about puppies bought at a store - I am not from the states, but from Denmark, but I have noticed a lot of talk about sickness in puppies from stores. Maybe it is because they are raised in puppy mills...
I don't know what you can give your little dog to eat when she is so picky. Yorkies are very picky by nature and I went through 3-4 foods before finding one my dogs liked.
Have you tried Royal Canine or Solid Gold? I think those are some of the more popular foods to give your yorkie.
Best of luck with Punkin!
(Do you have any pics of the sweetheart?)