I think the duck would do well to see a vet, if you can swing it. Sounds like the infection is systemic, so she will need some serious care (this is my gut feeling).
Cutting is not a good first resort, because it opens the foot up to worse infection. If there is not just one obvious place that is swollen, then I think treating with oral antibiotics might make more sense.
Cutting is not a good first resort, because it opens the foot up to worse infection. If there is not just one obvious place that is swollen, then I think treating with oral antibiotics might make more sense.