How did the vet diagnosis the food & shampoo allergy? I hope you can get things straightened out quickly for your girl.
I would recommend that you do some reading about dog food. There are many better choices than Eukenaba. I know the vets encourage this - but often it is because they are selling it. Here are a few things you may want to read
Dog Food Report The Dog Food Project - Dog Food Label Information 101
The entire Dog Food Project site is very interesting
This is a site that rates foods - remember that it is someone's opinion. But here you will find a list of ingredients for just about every dog food made & available in the US. I would recommend finding a 4 or 5 star food off this list. Some people will use a 6-star -- but many think those are too high in protein for a yorkie
Dog Food Analysis - Reviews of kibble
Here is a thread with info on contacting a lot of companies for free samples. I emailed most of them. You will be surprised how generous they can be about sending out samples
http://www.yorkietalk.com/forums/yor...e-samples.html
Also, homecooking is a good choice for a lot of people - that way you have control over what your dog is eating. Here is a lot of input & recipes
http://www.yorkietalk.com/forums/yor...od-treats.html
Good luck - hope your girl feels better soon