Poor other mumma duck, at least she'll get a chance next time :). Great news that's she's now accepted the new comer I guess your ducks are learning how to be mums as well.
How exciting! I don't have any experience with hatching with ducks but I have incubated quite a few of them. I do wish my duck would sit on her own eggs it would save me a lot of heart ache when I sell the ducklings and also a lot of worry of being responsible for them. I'm sure ducks are a lot...