she is definitely a beautiful duck! how's she doing without her buddies around? mine always cry for one another.

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She has something stuck in there.
Maybe its time for a drawing poultice. While its open is a good time.
Please tell me what her environment is. IS there a chance she can have metal fence fragment, stone, or even wood or bone fragment in her foot? When it happens to a dog, they get a swollen area that is difficult to heal even with antibiotics, much like you've described. (They get it a lot) With a dog, they have soft flesh and pad, so the object (usually a weed seed) works in one side, and out the other. A duck has much more difficult skin. Its meant to prevent this, but when it gets in it can be difficult to remove, and will not responds to antibiotics until the foreign matter is removed. Antibiotics fight bacteria, not foreign matter.
If you want to be 100% natural, I suggest a potatoe poultice. Simply cut a potatoe in half, and use a dull knife to scrape up pototate mash (kind of like mashed potatoes but with raw potate) to about a tablespoon size qty. Clean the wound (just rinse it - I'd stop irratating it with alcohol for a day), place the potatoe OVER THE WOUND NOT into the wound; That is very important. Place an absorbent bandage (cotten balls or pads) gently but firmly over the wound. wrap it well, so it won't move around. Put her back in her pen, but keep her feet dry. (I'd use a milk jug w/cut out hole for her head about 1/2 way up so she can drink, but no spills) In 12 hours, removed bandage, rinse with sterile water (boiled and cooled w/plate over it). IF you have them, sterilze a syringe (no needle) w/the water. Pop it in, seperated, and boil gently for 10 minutes - cool. Use the syringe to spray the water into the wound, if it is still open. Poultice again.
On most animals, when the irritant is gone the whole will close quickly. Don't reopen it. Usually the irritant is found in mucus, blood, and pus from the wound. Use a toothpick to examine the blackend poultice for irritant. I would do this every 12 hours for 2 days (4 treatments). If irritant is found before then, discontinue. Just lightly use neosporin cream (not ointment, it hold in bacteria) over the closed wound after final treatment. See if she has improved in 24 hours after last treatment.
The swelling should go down, and the wound will close, most of the time. Please fill free to PM me if the need arises. I'll check back for updates tomarrow.