I think - just from the few times I've tried - when they are laying and determined to sit, she will dash out to check everythings ok, sit for a while, lay another egg, tidy up a bit, cover it a wee bit and go off for the day in her usual routine - if she has her clutch (my girls seem to wait for absolute minimum of 4 but we also had one that waited till 12 eggs!! and she hatched them all) then she will sit on the nest all day and night with only a couple of breaks of about 10 mins to eat, drink and a quick swim. If she's sitting on the eggs all day today then I would give it a go this evening when you put her in - it's worth a go to me. It's not nice but I would rather loose a few eggs than the lovely ducks we have. I have done this and it's worked, she sat straight way on them no problem, but also had one nutter that scattered all the eggs all over the place and didn't approve at all - not sure what goes on in their heads - but I guess they don't know what I'm thinking either - good luck - ducklings are just great - best get all the extra feeder and water container down from the goat house loft!!