Peep, you'd need to introduce the duck the same way you'd introduce a new hen. Slowly. Especially with a bunch of grumpy old hens! BTW, the squabbling over a nest box is normal, lol.
Say I had a pen or run and was attempting such a move. I'd take wire fencing, separate off an area inside the...
Best of luck finding her a home!
BTW, I have 22 chickens in 3 separate areas- due to a overload of roosters, 5 bantam roosters share a pen with 3 domestic Mallard ducks. Aside from the muddy mess the ducks make, they are all getting along great, after 4 months together.