I'd take a syringe with out a needle ir a dropper and try dribbling some of the electrolyte water along her bill of just inside her bill {never down the throat] She may be dehydrated you could also try making a soupy mix of her crumble and warm water and try using syringe or dropper to get her to eat a little. She def needs to eat and drink very soon.
It sounds more like it could be "limber neck", which can be caused by botulism, to me. Leg weakness can also be a symptom: http://www.merckvetmanual.com/mvm/poultry/botulism/overview_of_botulism_in_poultry.html.
There are a number of possible ways waterfowl can contract botulism - through food, water, wounds. This article has more info: https://www.beautyofbirds.com/botulism.html. Without testing, it would be difficult to pinpoint the cause (and the pathogen).
