Update: Marshmallow is fitting in just fine. She hasn't really integrated with either of the two groups we have but she's very sweet and friendly to us. She's healthy and seems happy to be free ranging around our backyard. My hope is that she'll eventually become part of the group of the younger chicks - she's probably about the same age. This is the group she kind of stays near. In the evenings when we sit outside, she comes and hops up on the patio table to say hi. We did have a bit of an issue getting her to figure out that she needed to go in to coop and roost with the rest. For the first week, we found her up on the pergola 3 times, and up in a tree a few times. Each time we got the ladder and put her on the roost with the others. For the last few nights, she's been going up herself so things are all good.