Help! My duck is eating her babies’ shells

[MsMonica22]

Help! My duck has been incubating eggs for 30 days now. She has hatched 2 and has 4 more underneath her due to hatch next week. She started eating the shells of one under her, which killed the duckling.
She has oyster shell, food & water in her duck house.
Why would she do this?
I did take 4 eggs shells out for her eat. Anything else I can do?

 

[Meatpies]

She might be an egg eater. Maybe use an incubator and separate her from the eggs and return them to her after they've hatched. She could've broken the egg and accidentally took a bite from it. I've read from this website last year to put fake eggs in her nesting box from when my chicken ate her eggs on a daily basis. Sometimes the habit can go away on its own. Is it only that one duck eating eggs?

 

[MsMonica22]

She might be an egg eater. Maybe use an incubator and separate her from the eggs and return them to her after they've hatched. She could've broken the egg and accidentally took a bite from it. I've read from this website last year to put fake eggs in her nesting box from when my chicken ate her eggs on a daily basis. Sometimes the habit can go away on its own. Is it only that one duck eating eggs?

Thank you for your speedy reply!
Yes. She is the only one.
I don’t have an incubator and I’m trying to let nature be nature and not try to play God, but my human nature wants to say, “You’re not doing it right!” Lol
So far, she has amazing with the one duckling.

 

[Meatpies]

Do you feed her shell grit or layer feed? Sorry for the late reply.