Aww, sorry about your duck...
Four or five days ago one of my cayugas went totally lame!
I was really freaked out, because she was really weak and couldn't walk to get food or water, so I moved her around to the water/food all day and hoped for the best. EVEN BETTER (sarcasm), it was pouring rain all day and night the day she went lame. Three days of keeping her near food and water and a night of searching for her because she had wandered off and couldn't get back, and now she's pretty much fine.
It's like you shouldn't give up hope lol.
I didn't think she'd be okay so fast, and I still don't know what happened...
The to top it all of my goose died yesterday!
THAT was unexpected and horrifying...
Hope you don't feel too bad, sometimes you just get weak ducks.
Keep your chin up and maybe you can try again in the future.