I'm not located near a pet supply store or a vet that knows about ducks. Also the other female duck is starting to have the same wound on her foot. Thanks in advance for any thoughts that might help her from suffering. With bumblefoot in chickens, we recommend cleaning the wound regularly and packing it with triple antibiotic ointment. Check it every couple of days to confirm progress and retreat the area.
Ducks can have antibiotics.
I hear from our vet that many of the antibiotics effective in poultry are being withdrawn by FDA or USDA because of resistance issues. Hope this helps. It is called Baytril. It can also be used on pheasants. It is true that waterfowl should not be given mediciation unless necessary.