I've had to add new pullets to my flock a couple times now (and this also applies when you take one out for a few weeks if you have to doctor it). I put them in runs right beside each other where they can see each other through the fence for a couple of weeks. Then I let them free range together for a couple of weeks, starting out just a couple hours in the evening and working up to all day. The last day, let her go in to roost with the others. They'll duke it out a little over who's gonna sleep where, but that is normal. When they wake up in the morning they should pay her no mind. Also, you want to put them together when they are very close in size. Don't put a tiny pullet in with full grown hens. They'll have too much advantage and likely kill the smaller bird. Good luck!
(Amazing how much drama goes on in the hen house, huh? Perhaps that's why they sometimes allude to a group of women as old hens.
My hubby regularly sees such pecking order going on at work.)
