I still don't know what was wrong with one of my duck, Crackers, but she had a bad leg for quite a while. It seemed like it got worse and worse and then got better and then worse again. Much like you, I couldn't bare the thought of taking her away from her friends because she and them would cry so much. Sometimes I worried that I had made an awful mistake, she would try to run after them and just couldn't make it, so I would pick her up and take her where she wanted to go. Eventually I put the feed up by the pond so that she didn't have far to go, but she would get trampled by everyone. Or she would lay down and everyone would want to cuddle up with her and they would step on her, and she would have to keep moving. It was so sad sometimes to watch. Still I couldn't bare to separate her.
At it's worse she couldn't use her bad leg to paddle in the pond, though she tried. She spent a lot of time in the pond and I had to make a special way for her to get in and out.
I also gave her poly-visol once or twice a day depending on how easy she was for me to get. If she spent too much time trying to get away from me, I would just skip it.
It seemed like it took forever, but in the end she recovered, and today the only thing that lingers is that she has one foot slightly turns in. I think that came about from her hobbling around.
You of course know what's wrong with your duck, but here's a thread where a few of us talked about our gimped ducks:
https://www.backyardchickens.com/forum/viewtopic.php?id=217224