Brandy, I just scanned over everything in your thread, I think this qualified as an Emergency for sure! How upsetting for us when we see our ducks in trouble!
My $0.02:
Epsom Salts are cheap cheap cheap therapy for a bunch of different problems, infections, swellings, bruising all included. Why not? Personally, I had a duck with a limp, swelling and Bumblefoot, I was not able to manage the compresses and keeping the leg clean (due to mud!) and *Eposom Salt Soaks cleaned up the problem quickly!* 2 days, to be precise. My personal theory is (for ducks, fish, dogs, cats, humans, you get my point): Why resort to antibiotics if unnecessary? Get your duck some spinach from the grocery, add some water soluable vitamins from your LFS (I use
MannaPro), provide duck with calm care and it may just surprise you and spring back. If not, well then you will need to make a decision on the most humane way to deal with the situation. The advice you have been given by previous posters is very good advice, and I sincerely hope and pray that your duck feels better!