Dior doesn't pick on the new duck does she? she for sure? Maybe introduce through fencing for a couple of days just so they get use to each other. And another idea why not bring home 2 ducks that way if something ever did happen to one there would still be two to keep each other company.
Can you trade her for another from the friend who has a large flock? Surely another one wouldn’t have the same issue. A duckling wouldn’t be able to be with Dior till fully feathered So she’d still be alone for at least 5-7 weeks