Well, right after I posted this, I was so anxious and concerned about what they might be eating and filling up on I started trying to locate a number and name for the lady. Another woman right behind me across the lake used to feed the muscovy ducklings rice. Mine were younger then and didn't go very far into the water.
One thing I forgot to mention though, those muscovy ducklings are big now too, and she's been feeding them as well! Boy are they eating well! Them and the Mottled ducks!
Anyway, it was going to be hard for me to ask her not to feed them. Since she's feeding them all and of course mine have decided to join in on the meal. 
I called her and we talked. She was very nice, but given the circumstances I felt like the most I could do is make sure she's not giving them junk. She did her homework and she only gives them good food. It was funny, I explained that the ducks are my ducks, and she referred to the muscovies as her ducks!
But at least she's feeding some sort of feed. It has corn in it, and I guess they must like it better than my food. But I can't imagine they get a lot though. All the ducks hang out there now so she has a lot of mouths to feed and from what I could see using my handy binoculars 

 she's only coming out with a few cups or so of food. I know they always have their heads in the water eating other stuff too. They must really like it. Maybe that fills them up too. But I was under the impression they would always depend on me for food since I raised them.
I think mine ended up down there because they've started following some of the other ducks. Mine are drakes, 4 of them. Maybe they're following girls. Who knows. I know they'll never catch them! Plus they like sleeping at the waters edge over there because the trees shade them from the sun.
Right now they do come home every night. They head home at dusk and hang at the edge of the lake until dark and the lights come on. Then they make their way in. We don't have to call them anymore, so that's good. Because they've stopped coming to my call unless they're in the mood and want treats. Not sure what to do about that. So I'm keeping my fingers crossed they keep coming home on their own.
I asked her to call me if she ever sees something I should know about. And if they ever do stay around after dark to shoo them home. Explaining that they can't fly and are very vulnerable.
All in all, it's good to have another set of eyes on them now that they go so far. And to have another duck lover too. A lot of people have taken to watching and enjoying them on the lake now that they travel farther. They're the only white ducks out there so they're pretty popular. With their little wigs!
Thank you all for your input.