I would put a quarter teaspoon apple cider vinegar in a half gallon of drinking water.
I wonder if there's a recommended concentration - ACV has electrolytes, but I am not sure how much is too much….
A photo would help.
She probably has/had hypothermia.
I would get some electrolytes into her water. You can find poultry electrolytes at many feed stores. Unflavored pedialyte without iron is another option - there is dosing information in the archives here on BYD Duck Forum, I am pretty...