I have had both ducks and chickens and I feed them all the layena laying crumbles/pellets they make for hens. The ducks do just fine with it. Just make sure to not feed ducks the medicated chick starter, I have read that it will make ducks sick. I bet the hens would also all be fine with eating...
I think she is too old to imprint on you, but she can still end up being a very friendly duck if you spend time with her. I have a mallard I got when he was an adult and he still follows me around. Just hold her and make sure she sees who feeds her and she should end up being friendly. :D