Poor little girl has had her whole world upset, fortunately chickens are forgiving creatures and she should get over the trauma pretty fast. Now getting the old girls to accept her, hopefully it will go pretty fast even if she is quite a bit younger since she is a fairly bossy breed. Keeping them separated like that with the two pen set up you have for awhile should work fine. I would keep that up for a few days at least (you want the new girl to feel more settled anyhow) and see how they behave with each other across the fence before putting them together again. Do you have any different place you can let them out together where they can't get away? When you do put them together, for the least drama, it is usually best to either have them on neutral territory (where neither old nor new chicken is at home) or put them where the new one is, so the old ones are not at home. When you do put them together overnight, be careful to open the coop up really early in the morning, you don't want them locked up in a small area if they get into a fight.
If it is easier, you can keep the little one in the dog crate or a box overnight, just put some shavings on the bottom and cover the crate. Chickens are so easy because they do that zombie thing when it gets dark, you can keep them about anywhere.
Sounds like you guys had quite an adventure chasing a new chicken around, you're not a true chicken owner until you've spent half an hour chasing a chicken through the underbrush.
