TI like the sling idea the pic was posted earlier. I am sure if you google you can find all kinds of ideas about how to make her mobile by making a wheel chair for her or a sling on wheels so she can push around with her good leg. If she seems happy and not in pain and your willing to take care of a house duck then I say go for it. The duckling is adorable.
Looks like quite a bit of swelling in both legs above the ankle are they hot to touch too like infection in them?
What have you done so far to try and help?