Niacin, Niacin, Niacin.
Was your vet giving shots of B3 specifically? or another form of vitamin B (Riboflavin is B2)? It should have been B3. I'm sorry but I think your vet is wrong.
Start giving her Niacin. Make sure her feed contains it. Give her some "Sav-A-Chick" electrolyte (from Tractor Supply) added to her water that has it. Get some Brewers Yeast (not bread yeast) to sprinkle on her feed (contains Niacin). If you can't seem to find Brewers Yeast check with your local health food store or a place that sells beer making ingredients.
I will check, but I believe the yeast used to make beer is not what we call Brewer's Yeast - please be patient, I'll be back after verifying that. I believe Brewer's Yeast is spent - not active.
Okay - I can see how it gets confused. The brewer's yeast to take as a B vitamin supplement has been used, and there is no active yeast culture in it. Brewing yeast, sometimes also called brewer's yeast, has active live cultures and is not good for eating.
Edited by Amiga - 11/4/15 at 9:25am