I have a flock of 13 RIR, 1 rooster and 12 hens, that are all free-range. For the last 4 nights, when I go up to close the coop, there is always 1 hen that hops onto the branch of a hemlock tree beside the coop instead of going in with all the others. I always pick her up, and put her inside the coop with the rest. During the day, she mingles fine with all the others. No one is picking on her that I can tell. Why won't she go in with the others at nighttime? What can I do to break her habit? I'm afraid that she may start going higher in the tree where I can't reach her anymore.