adding smaller birds to flock

[cluckers73]

I have my girls in a chook mower, I went from 3 chooks to 2 as one was a Roo and can't have them where I live. My 2 older girls are BL and my new girl is a PR, with the dates I was given there should only be 2/3 weeks between them. My new one makes the older 2 look like Galioth. I placed the new one in with the girls for bit under supervision... One hen I felt a bit heavy foot & and yes had a peck at her, she did seem to mind being around them. The little one I have had in the brooder at night in the garage, last couple of days I have had her in a collapsible carrier outside the chook mower so they can just get use to her. Yesterday I put one of the big girls in the play pen, went back to get the other and she was trying to have a go through the cage, there was a yelp from the small one. Later when I had checked her, there was I little nick near her eye, not enough to be bleeding. I can't let them out to roam yet without supervision till I get under my fences covered in to stop them getting out.

What else can I do to ease this transition?