It sounds like it is a protein losing enteropathy...could be lymphangectasia. I had a pup with that...she lived for 5 1/2 years. I lost her recently but not because of that condition...she developed cancer.
She was on prednisone when first diagnosed .. then they were able to taper it off. Hopefully that will happen with your Zoey.
Did they discuss the importance of a low fat diet for her?
Here is a link that might be helpful:
Intestinal Lymphangiectasia - Mar Vista Animal Medical Center