Welcome to BYC. I have Muscovies and I would not let her sit or have any young ducklings. They do not always take to them and can possibly hurt them. I would lock her out of the coop and if you are concerned about her flying off clip one of her wings to stop that. Mine are clipped and don't go anywhere and I remove the eggs daily so that they don't stay broody. Good luck with yours, I am sure she will do fine without any babies.