I usually keep em separate for a while in a separate pen where they can see each other. As soon as they seem to mellow out and stop clucking irritably I usually introduce. I temporarily add an extra feeder and waterer in the corner because she may need it, the original hens may run her off when she uses community feeders. If you throw feed then throw some in whatever corner the new one hides in. They will eventually tolerate the new addition. Now she may have some troubles but its not all bad, she will just have to figure out where she's at in the pecking order. Just make sure its not excessive, if it is then separate the offender not the new hen.
I made a simple pen out of lathing wire for stucco, got it at home depot, (cheaper and tougher than chicken wire) and cut out a 6' piece. I rolled it into a round pen and used fence clips for chain link to attach ends. Just cut out another piece for top. I ran a broom stick through it for roost, drilled holes in the ends and zip tied it to the cage for stability. I use a disc snow sled for a roof and I made a small nest box to go inside. I also use a 1 gallon waterer and I throw feed them in this pen. It keeps them more active. I also use old tent stakes to keep it safely on the ground. I keep 3 of these for various reasons; they're great for either hospital, segregation, introductory, or observation pens.