She may not be eating much. Some ducks are like that. All you can do is offer it to her. She may not recognize it as food, by the way. Can you get mealworms?
Moving them may not be such a big favor. You don't know what predators exist at the other location, I would guess. It's a tough, tough bunch of choices. Yes, crows are dangerous for ducklings, or at least they can be.
I hope more folks can check in here with some ideas.
I don't know much about wild ducks but have experience with other wildlife. I would suggest not feeding at all. You really don't want Mom or bfabies becoming dependent on free food.