So very sorry this happened. However I disagree with your Vet about the liver shunt.
She SHOULD have her Bile Acids Tested as this will show liver function.
She COULD have an LS or MVD and it could show at this point. Given the fact it happened after eating and that she is very, very, very tiny. I would be very surprised if it wasn't related to liver function. The kind of food is very important. Euk would not be good for an LS or MVD dog.
The BAT is a blood test, costs about $80, you get results the next day.
Please have this done
...My Roxy was 3 when she was diagnosed with MVD (tiny little shunts in her liver). She has to eat special food and take supplements, but she is doing ok.
You might want to join this group too:
DogLiverDisease : Dog Liver Disease
This is a group of wonderful people that are not only terrific for advice and support, but there guidance with experience and a tremendous amount of research is incredible.