Hardware Disease is what I suspected all along but the description in Storeys wasn't all that clear. It must have been something she picked up in the yard while foraging. I was HOPING whatever was troubling her was treatable, but I suppose not. I am becoming more confident that's what it was. I just found this excerpt from duckrescuenetwork.org that pretty much sums it up.
"Hardware Disease- Ducks and geese are attracted to shiny things like pennies, screws, nails, staples, coins of any type and other metal objects. They will swallow them. This is extremely dangerous and most often fatal. As it is digested, the metal (and coating on various metals) poisons the bird, harming the kidneys and liver. It can take days and even weeks for any symptoms to become apparent, at which point it is often too late. Early symptoms of hardware disease include a bird that keeps to itself, away from others and eats less." She was definitely acting like this...I described it as withdrawn or "depressed." Poor thing.
It makes me feel sad to think of it, but I think when I brought her in, gave her the bath and was messing with her (cleaning, petting, massaging...)and palpating her body to feel if anything was amiss I might have caused the object to do her inner harm. It was after that when things went quickly south. So sad for her to go this way...but I suppose there's no good way for it to happen. We just wish we could have enjoyed her a bit longer. Poor sweetie never even made it to her 1st bday.
i'm sorry RIP Chewy. having to give up your ducks too 
maybe you could find a rescue centre??? i would take them but obvious distance problem and i already have 2 drakes 
