How to keep the serrated edges on duck's bill worn down

[WhiteTreeOfGondor]

I just noticed that the serrated edge of my duck Emma's bill has grown longer than usual. I couldn't get a good picture; it's more noticeable in person. She has been penned in a small area to heal from her broken legs, so I think she must not be able to forage enough to keep her bill worn down. Are there specific foods or anything that would help her do this? What things do they forage that naturally trim their bills?

 

[Fluffy_Moth_With_Silkies]

They normally forage for shelled creatures in the water; crustaceans and such. But I'd just give her a plant to eat on that might help. (I don't know which one.)

 

[WhiteTreeOfGondor]

They normally forage for shelled creatures in the water; crustaceans and such. But I'd just give her a plant to eat on that might help. (I don't know which one.)

My other ducks don't have a natural pond either, but maybe snails are their substitute. They're always looking for things on the ground and in the mud; I just don't know what they're finding most of the time .