I remember another post you made about problems with her back legs not long ago. I've seen a lot of dogs with neurological problems and this really sounds like a neurological issue now more than ever. When it comes to neurological problems, a typical vet often misses symptoms. I would take her to a neurologist (typically a university) and have them do a neurological exam on her and possibly a MRI. It's common to have diarrhea and vomiting after a seizure but not for this long! Did your vet mention the possibility of an inflammatory brain disease which is common to the Yorkie?
In the long run, its less expensive to get the right diagnosis. Here is a list of veterinary neurologists by state and city.
http://www.acvim.org/uploadedFiles/p.../Neuro_Geo.pdf
Your vet will need to call in the referral. Another option is to have your vet call a neurologist and do a phone consultation.
I wish you all the best and will be sending out prayers for both of you!