Based on the photos of the chick, and of the Easter Egger, I think the chick probably just came from the breeding pen with the Easter Egger rooster.
That rooster should produce pea comb chicks. I think he probably cannot produce single-comb chicks, but I am only about 75% sure of that.
I think...
Blondie does not look right to me.
Buff Orpingtons are not supposed to be that light. Some chicken breeds are known for producing not-right chicks of certain types, but Buff Orpingtons are NOT known for producing birds like that.
So she might not be a pure Buff Orpington. She might be an...