Rescued a Barred Rock today--feathers really picked--need help

Today I adopted a new chicken...she's about 7 or 8 months old and her feathers are really picked off on her back, bottom and even her wings. I have 2 other chickens at home--a Sussex and an Orpington, each about 8 months old also but bigger than the Barred Rock. The BR I rescued came from a home where the lady had over 300 chickens in a very small area. All chickens were missing feathers to an extent...some more than others. The older layers, like the one I chose, were especially "picked". As ugly as she was, I just couldn't pass her over for another "prettier" chicken--I felt that she needed me to rescue her. So now she's home with us and I've got her in a huge, open dog kennel inside our large coop. I've given her lots of treats and she's already acting full of life. How long do I need to keep her segregated in this cage within the coop? She's lived in awful conditions for so long, I want to let her free range in our large yard as soon as possible. At the same time, my Orpington is fairly "territorial" and I'm not sure she'll react well to this new addition. How can I keep my other 2 chickens from picking on her? I just want everyone to be friendly!! Advice please?