I too have a white unknown breed with her tail down. She lays fine, eats well and gets along with the other hens. I bought a chicken coop that came with 7 hens and she was like this since I got them (1 1/2 months ago). My inexperienced guess is it was broken, but maybe it's genetics....still...
I've just bought my first coop & flock of 7 hens, about 4 months old. One of my girls, who is one of two that just started laying, has downward tail feathers. When we got her she was this way. She is acting normal, eating fine & otherwise looks healthy. An suggestions on what's going on?