I'm so glad you have a vet to consult with to help guide your decisions. I just wonder what determines infection over a fracture or sprain. Did he narrate his observation and diagnosis?
Bruises do something similar when you press and release them. But so does infection, so it's hard saying. I'm just wondering if she sprained her ankle in response to the growing sore on the bottom of her foot.
I only know the injuries I'm treating on my rooster. This is where others can help...
Feet are treats to treat, let me tell you.
But ducks love water, and from everything I've read on bumble foot, and from my own experience treating a rooster with a badly swollen ankle joint, it's my feeling that an epsom salt soak at ten to fifteen minute intervals, three to five times a day...