Oh, she's so cute! It must have broken your heart to take her back and then find out she passed.
This is the other possibility that I can think of. I'm no expert, though.
http://www.vet.utk.edu/clinical/sacs/shunt/faq.shtml
After you read that, then you can read this:
http://www.yorkielane.com/BadBreeders/bad_breeders.htm