Ruth, I'm so sorry for your loss. But what a wonderful husband you have! Don't you just love it when these big tough guys go and do something so mushy and sweet?
I admire you for being able to free-range the way you do. Sounds like you are on the right track with Lucy. We have a big retreiver/shepherd cross that's just fascinated by the chicks and ducks, but I can't tell if that fascination has any aggression in it. We do the same thing, hold the babies up to her and speak softly and pet them both. She was an abused dog as well and once she decides something is part of her family she is feircly protective, so hopefully that's the way things will go with the chickens and ducks.
I had to laugh at your description of the little ducks moving as fast as football players. Ours are the same way! What little buggers to catch! We've only let them loose in the house, but when they break free they can really move! Our little black cayuga is so fast that my daughter named him Zipper!
Best of luck with everything. It always works out the way it is meant to.