I agree that they should be trapped and humanely euthanized. They're disruptive to both you and the environment, they can no longer survive on their own, and nobody's going to want to adopt or buy diseased ducks. It makes me sad, but it seems to be the best option.
It sounds like he drowned her. Drakes will push the ducks' heads underwater in an attempt to make them submit. If you get a duckling, don't let her near Chuck until she's full grown. And I'd get another pekin, or even jumbo pekin so that she'll have a chance against him in size. I'd go back to...
I used a Brindea mini Eco incubator if my drake ever went broody, that's make my year.
By the way, my new rooster did his first crowing this morning. What timing!