A Broody Duck

One of our ducks has gone broody. I had thought this might happen to one of the chickens, given that they now have a cockerel, but no-things always happen a little differently here, and for us, it's the duck. For the last few days, we've been lifting her off the favoured egg box after about 10.30, and shutting her out of the coop. Sometimes, I've just lifted the nest box up vertically to turf her out (and yes, tesco's do deliver their shoping orders in very similar baskets), and at other times I have called upon any ill-prepared sandal-wearing man in the vicinity to do the deed, whereupon he gets his toes pecked. Today, I gave up. I have lost out to the forces of nature. Whenever I go in the coop, this duck gives out an odd chirruping noise by way of a warning. She is currently sitting on 3 hens eggs which are probably fertile, and one duck egg which i don't think possibly can be. I've looked on the net, but still can't see any advice for what happens if a mother duck does hatch baby chickens. Will she try and take them on the pond??? For the moment, I'm just amazed at her commitment. Usually, the ducks are very sociable and wander all around the place, and especially love to know what's going on in the house, but now she just sits there all alone, in the darkness of the coop, gazing at nothing, and just listening to the buzzing of a fly as she sits and patiently waits...and waits...and waits....