integrating duckling into flock

Hi. We started keeping ducks a few years ago. We have 4 (now 5) Ancona breed ducks, 3 females and one male. One of our ducks is very broody. Last year she sat on a nest and we had 3 hatch out but found none alive, sadly. She tried again this year and had only one hatchling, but she (or he) did...