Sick duck need help!

So my duck has always walked with a limp but this past week she has gotten terrible. Dont wanna get rid of her but ya know. So when she walks she like falls backwards like she is over extending her legs her neck is also all wonky and she vant hold her head up, white eyes, diarrhea, when she falls backward she is not able to get back up so a few times i find her on her back paddling.

What is she eating? If she's eating chicken feed, she likely has a severe niacin &/or b vitamin deficiency. Try giving her some brewer's yeast. It won't likely go away right away,  but if that's the problem, you should start seeing at least a bit of improvement in the first 48hrs. The problem, of course, is that it could be something else, entirely.

Along the lines of Carla's suggestion, if she's just been eating store-bought feed, try finding some live food for her. Bugs, worms, snails, etc are all good and a vital part of a duck's diet.

Oh, and welcome to permies, by the way! I hope we find the solution for your duck.