donrae
Rest in Peace -2017
The hen pictured is a mille fleur leghorn--thus the light body.Swedish Flower Hen? Of the breeds you posted, that is all that I could figure this one is. As a breed ... or rather as a "landrace" chicken, they are not all big hens. There is no absolute standard on size for them from what I understand. I would certainly consider a Swedish Flower Hen of that size to be quite normal. But maybe I am missing your point?
She's a pretty one!
Were the Rhode Island Reds, Blue/Black Copper Marans, and Buff Orpingtons as small as the hen above? If so, then ... hmmm? Were they all hatched at the beginning of April? You didn't leave the lights on all day and night past 8 weeks, did you?