Hello! I used to have a call duck named Patitas, She used to have this type of thing where she was mostly dirty, Never quacked, and sometimes refused to eat, I usually gave her some calcium and electrolytes and she went back to normal, and I would recommend (Unless your vet says otherwise) To put some electrolytes in her water, Another reason why she might not be swimming is that she might be a bit scared of doing so, I used to shower her with water back when we first got her and she grew to hate water because I would randomly do it I wish i did not do that and let her go in water whenever she wanted to, She would drink it yes, But she would not jump in it unless I put her in it. I have another duck who will go swim in water whenever she pleases to, Another factor might be that she may be getting picked on (Highly likely) or she is lonely for a mate (Highly unlikely but still a possibility) I had a rooster who would try fighting her because she was just small this made her scared to eat or drink because she thought she would be attacked (Our rooster is very territorial over food), We separated them by keeping Patitas inside for a few days and when we put her back down the rooster no longer bothered her, If you keep any birds with her I would check if any are picking on her, I would also recommend putting up a camera in her coop to see how shes doing. She may be experiencing common sicknesses in call ducks because they are very fragile to illnesses and need a lot of tending to so once again I recommend putting some electrolytes in her water, and Feeding her more calcium in case she is egg-bound. Some pictures of how Johnny looks may help