They are so cute when they get broody! This is what my broodies do:
They find a little nest spot (be careful it's inside a safe place, you don't want anything to kill the duck). They fix it up a little, they get really crabby, they stay put in the shelter longer than anyone else does, eventually they refuse to go outside except once in the morning and once in the evening. If you get near them they hunker down, hiss, give you the stink eye.
When they make their brief trip off the nest, they run outside, drop a big pile of poop, eat, drink, sometimes run around like mad, and then go back to the nest.
i have all my ducks in one big run during the day but i put them in at night in the coop for safty. i'm hoping she will pick a spot in the coop to make a nest. if not i guess i'll build something around her and her nest lol