Egg Bound?

I have recently lost a long loved hen, Lupine, and I don't really know why. We now have six hens and a duck, and our duck recently learned he's a guy. He lost his siblings at the pond they lived at, so we moved him in with the chickens which has been great, until he started trying to make babies with them. They are losing feathers like crazy, and I don't know if it has anything to do with Lupine's death.
We'd been on vacation for two days, and I left our flock with lots of food and water. When I got home, I went to check on the chickens, and Lupine was flopped on the ground. She was breathing, but she was floppy and fell asleep every few seconds. I brought her inside and kept her in a shoe box, I hydrated her and fed her as much as I could (which wasn't much). In her shoe box, about two hours later, she let out a gross smelling liquid, and did it three or four more times over the course of the evening and night. She had lots of mucus and finally had convulsions and died. I would love to know if you have any ideas as to what happened and what I could possibly do if it happens to any of my other hens. (Also- tips on what I can do to stop the duck? It's at the point where we might have to give him away to protect our hens)
Thanks so much!