No need to seperate her because she'd be lonely without her pals, and the Niacin will be good for all of them. Plain Niacin is getting harder to find, so you're best bet is most likely either Brewer's Yeast or Nutritional Yeast, which you can find at grocery stores, or even Walmart usually. If it's the plain Niacin you seek, I found mine for Cas at a local Vitamin store that carries nothing but Vitamins and nutritional supplements.
The vitamin (just Niacin) would be dissolved in the water (100-150mg to each gallon of water) and the yeast would be sprinkled on their feed (I think it's 1 teaspoon to each cup of feed?).
Note: If you find plain Niacin, make sure it is the NICTONIC ACID kind, and doesn't say things like "time release", "flush free", "no flush", etc.
Thankuou for the information Will go out and try to find some today hopefully she improves!