Female Muscovy Cayoga
Featured Stories on BackYard Chickens
It's hard to say 100% how she will take to a new duckling, however generally speaking Muscovy ducks are great mothers so I would be willing to bet she would take the duckling in and be accepting.
As far as the breed is concerned I would suggest Muscovy unless you don't care if you get a male from another breed and down the road they cross breed. Hope my two cents helps, good luck!