I know others have already said this, but it really sounds like she is lonely. If you could get a calmer, similar aged duck hen, as a companion, that may solve it.
Large flocks and isolated ducks tend to be the loudest. I only have two ducks, and the noise is pretty low unless something startles them. They just chatter quietly. They're so quiet that after a year the neighbours have only just figured out they exist!
I wouldnt suggest a muscovy, as muscovy are different to ducks, and communicate differently. A khaki campbell, or cayuga even, could be a little quieter though. If you end up choosing a flighted breed, you could clip wings.
I imagine giving her a friend could solve your noise issue. If it doesn't work out, you could always rehome the two of them after they've become friends. If that isn't a possibility, the only humane solution I can think of is rehoming her, which sounds like it would be a shame after all your effort to nurse her to health.