Hi chickorama,
She may look odd, but I feel sure she is the only one that could have laid it. The only other chickens with her are 3 leghorns which have all been laying white eggs, one polish hen that also lays a white egg, a very small black and white bantam (don't know the breed) that lays a tiny egg, 2 frizzle bantams that lay small ivory eggs, and 7 white Silkies that lay small ivory/beige eggs (when they're not broody, that is)!
Not only that, I have seen her sitting in the nest (several times) looking like she was about to lay just before I found the green egg in that same nest. I noticed that she has a funny habit of playing with the hay with her beak when she's waiting to lay.
The egg is much too large to be from the Silkies or the bantams and I don't think the others are good candidates, either!
I really feel certain that the black and white hen laid the green egg but I certainly appreciate your input! Maybe I have an "Easter Egger" in a rare color!
Thanks for taking the time to respond! Genie