Ditto jessiduck, if it is early on, application of topical antibiotic ointment twice a day for several weeks (I kid you not, but it works).
 
If it is already causing her to limp, then a warm compress with epsom salt water (I use a shallow dish with a rag in it, someone else holds the duck and I hold the dish and the foot) twice a day followed by antibiotic ointment.
 
Romy is having a problem this week.  Took her to a vet who somehow found and worked out a tiny, tiny splinter.  If anything is still in the foot it won't heal completely until that is removed.
 
Cutting the foot is a LAST RESORT in my mind, because then you must keep the foot clean and dry (this is a duck, remember) until the wound is completely sealed up, or risk  much worse trouble.
 
Still, sometimes surgery is needed, especially when things have gotten bad enough to need to do that and get the duck on oral antibiotics.