After this experience, why don't you just wait for your duck hen to go broody? As she has already started laying, she might just need some time to collect the right amount of her eggs to set on.
Forgot to mention earlier: Be aware that a broody chicken hen might kill the ducklings after hatching them, as she might recognize them as alien = wrong kind of peep = no chicken chicks. So have a brooder ready just in case.