What type of wormer are you using? The problem with mixing wormers in the water or food is that it can make it taste bad, then they won't eat. I don't know that that is the case with your chicken. Feed some xhopped egg or tuna to get her eating, and put fresh feed out. My chickens love when I put a bowl of their feed and a lot of water in it to make it soupy. I recommend using a wormer such as SafeGuard Liquid Goat Wormer or Valbazen orally which you will know they have gotten the right dose. If you want dosages I can give you them. Have had your chicken tested for worms by taking in a fresh sample or two to your vet, or have you seen worms in the poop? Round worms are the ones most commonly seen, but there can be other kinds unseen as well as worm eggs. Poop pictures are helpful. Doesit look like there could be any egg-like material in it? Are there other symptoms you are seeing?