I am having a similar problem. It is not just one of my hens that is getting pecked, we have 15 hens (3 are 2 yrs old rest are almost 1 yr old). There was no major issues until we got a huge amount of snow, and the girls have been staying in their coop (their choice, they can come in and out of the coop as they please). There are a few hens that seem to be fine, but the majority of them now have patches of missing feathers. I watched them and noticed that my two older RIR are the most aggressive, but they also seem to have taught the others their bad habits! I have tried adding protein to their diet, it hasn't seemed to help at all. I am going to TS today to get some blu kote to see if that helps. I can't do anything about spacing until the spring, we were planning on making another coop anyway because we will be getting 15 more hens this spring. Any advice is appreciated. Thanks!