I would get her on antibiotics right away - something that can get into extremities - @casportpony does Duramycin do that? I apologize, I think I have asked before, and there's a bit of static in the attic these days.
She also could use an anti-inflammatory. I am not a vet, I am not a medicine expert, so I don't know about drug interactions. hennible's vet said a while ago that Advil was okay for ducks. Here are my notes from that post -
For ducks 6-8 lbs 25-40mg twice daily adult tablets cut up or children's liquid Advil 1.5ml twice daily, orally.
Amiga’s arithmetic – 8 pounds 40 mg is 5 mg per pound
6 pounds 25 mg, is just over 4 mg per pound
so, 4 to 5 mg per pound of duck
I would have her off the leg as much as possible - a lukewarm tub of water would probably help - now there's a two-edged sword - while we don't want the infection spreading into her bloodstream, I think improved circulation would help her fight the infection. Hmmmm….. another reason to get her on oral or injectable antibiotics right away - my guess is it's already spreading. Not to scare you, just to give you a heads up so you can do something about it.
If you are handy you may be able to fashion a sling (open in the back so she can defecate without problems).
Duramycin is sold by feed stores - call ahead. And we don't know if this thing is resistant to certain antibiotics. Without a lab, we cannot do a sensitivity test. We can only try something and if it doesn't seem to work, try something else.