Mama Mallard is not leaving nest
My Mama Mallard has stopped leaving the nest for any time period. She appears very lethargic. It is about day 14 in the incubation period. Is there anything I can do?
Washington County Minnesota poultry
My best guess is that she may not have been incubating the eggs before, and now she is. Ducks will not start incubating their eggs until they have laid all the eggs in the clutch, and they can only lay one egg each day. So, if she has been working on a nest of a dozen eggs, as an example, she would need at least 12 days (with maybe a day or two skipped) before she had a full clutch.
If that is the case, she will now sit nearly all the time, probably taking a half hour or so off the nest each day, and it will be 28 days from that point before the ducklings hatch.
If that is not the case in your situation, then I'm not sure what might be wrong. I think it would be unusual for her to lay a clutch of eggs and start brooding if she wasn't healthy. I'm not sure what to suggest, other than to make sure she has feed and water readily available.
Good luck with her!