Are you giving her niacin supplements? 100 mg per gallon of water, not no-flush or timed release, just a capsule emptied into the water at that concentration. It is a long shot, but worth a try, I feel. Also I would start some Epsom salt compresses on both legs. Don't let her drink it, it's a laxative. I put Epsom salt in water, soak a clean rag, and wrap the legs. Some others put the solution in a short bucket and stand the duck in the bucket. But no drinking!