How old are they? How much space do they have in the coop and in the run? Do you have any pictures of her you could post? You have just the three birds? Pictures of your set up might be helpful also. Boredom and over crowding are very common reasons for feather picking, and crowding is based on each birds individual personality and temperament, it can vary greatly from flock to flock and bird to bird. If you have a very dominant bird that is bullying then sometimes separating that bird for a period of time will reset the pecking order. In some cases people use pinless peepers on birds that pick on other birds. Adding space, or adding places for her to hide behind (and not be cornered) or get up and away, may help, or adding roosting space. Feather picking often happens on the roosts as they wrestle for space. The feathers may not fill back in until she molts, so age would tell when that might happen. Most birds will do OK in the cold unless they are really bald, some birds molt later in the year, in winter when it's cold, and usually do OK.
