Ditto, she needs calcium.
You can give her a quicker boost, also, by putting a teaspoon of calcium gluconate per four ounces of water and having her drink that. Many feed stores carry it. I order mine online.
It's tricky because generally speaking, drakes and non-laying ducks ought not to have too much calcium. But if she is deficient, I would lean toward temporarily boosting calcium in several ways till her eggs harden up.
She is possibly at some greater risk of egg binding, also, as well as other health problems if this is chronic.
Avoid giving her spinach. I have been told it interferes with calcium uptake. Are they on a layer feed? That's another idea. Many drakes seem to tolerate layer feed, though I would not recommend it except in a situation like yours.
And mine. I have a few ducks in my flock who just don't take up enough calcium from time to time, and I am currently continuing to improve their diet (currently feeding an organic layer with Ca gluconate added to water mixed in the feed) to improve not only calcium but also a wider variety of vitamins and components to keep them from having soft egg troubles.
Ducks are little individuals, so while you may read "ducks do this or that" remember there can be a range of what is best for each duck. Most of my runners have been just fine with their feed.
