Quatie
Free Ranging
I have bad luck with my Pekin eating oyster shells. If you haven't seen her eat them, you may to need to train her to eat them.And I recently started giving them oyster shells too, after a few soft shelled eggs.
I personally provide my ducks with oyster shells, some layer feed and duck feed. I find some of mine prefer the layer feed and overall are less likely to have laying issues with some layer feed on the side along with the regular duck feed.