Sounds like splayed leg to me, too. What kind of bedding do they have?
I would begin by making her a halter that would bring her legs closer together.
From Storey's Guide to Raising Ducks:
Causes
Spraddled legs can usually be traced to smooth bottoms in incubator trays, brooder floors, or pens where birds have poor footing.
Treatment
Provide floors with good footing. Tying a short piece of yarn between the patient's legs for several days will often cure spraddled legs. When hobbles are used, it is essential that they are not tied so tightly that blood circulation is restriced.
Prevention
Never put ducks (especially heavy breeds) in pens or boxes with slick surfaces.
The image shows a piece of yarn used as a hobble (loop around each leg, with a short length of yarn between the loops).