Bumblefoot - Infection of the foot
Bumblefoot is a bacterial infection of the leg that can happen in chickens and ducks. This can happen from a duck getting a small scrape in the foot, or puncture, and then swimming in their pond. Ducks are not as good about picking things out of their feet than chickens are.
You can tell first by them being lame and not wanting to walk around.
On physical exam, you will feel some heat in the leg or foot. This is usually infection or inflammation. Sometimes you can actually see a little bubble on the foot, this is usually the infection pocketing. Although, you may not always see this.
Separate you duck. This is very important for ease of treatment, as well as duck welfare, the other fowl may pick on her and she may try walking around to keep up with them and you want to limit her movement.
At this point, you can start doing Epsom salt soaks to help draw the infection out of their feet. Just don't let them drink the water, as this can cause diarrhea.
I would consult a vet to see about an antibiotic regimen to give to your duck or chicken.
There are several options, we did 15mg/kg of baytril twice daily.