I would encourage you to do the reading on that link that I posted before. It might be wise to purchase some duck eggs, to see it they will agree with your wife. They are a richer egg, delicious but some people get reactions with digestion, Some use GAS X, I use Ox Bile to help my gallbladder take care of the eggs`s natural fat content.I believe when people have digestion problems , it will show up when they eat duck eggs. Their gallbladder may need help with taking care of fats.
Ducks love to forage and are not happy caged up, they need water at all times when they have feed.Wire flooring is not good.and
housing them with chickens is not good either. Ducks are like pigs`s with feathers. they are messy and if your chickens have to share the drinking water, they will not stay healthy They can forage together but not housed with chickens.
When I had mentioned (light ) I meant light er in weight. a smaller duck will not eat as much as a big type duck. There is a type duck good in eggs and meat but they are heaver Ducks and chickens are both good foragers and they forage different. Chickens scratch and ducks drill.