My 8 year old lab will not drink any water. I took her to the vet because I noticed that she was licking her chops and sneezing, along with shaking her head. Her snout was also puffy. The vet said that she most likely was bitten by a spider or something and was having an alergic reaction. He gave her a shot of antihistimine. When I got home she ate her dry food, but will not drink or eat ice cubes. Do you think this is a reaction to the shot?

Could be the shot, the bite, or some coincidence. It is too serious to let go over the weekend. Call the vet in the morning.

You might try offering her a low sodium beef or chicken broth.