We have a sick hen, she is very lethargic and her comb has no color to it. She is also not drinking any water on her own. I gave her some vitamins and some water through a syringe. Any ideas on what else to do?
The symptoms you described could possibly be caused by external or internal parasites. Visually inspect her for lice/mites, especially around the vent area. Another possibility is worms. I recommend that you worm her with valbazen cattle/sheep wormer. Dose her orally undiluted 1/2cc, then redose her again in 10 days.
Sorry you lost your chicken. If it was parasites as dawg53 suggested you should really keep an eye on the rest of your birds. Good luck to you and happy holidays!