Introducing A New pullet to the flock

We recently brought two new girls into our flock, one is an Americana who is 6 months old, and the other is a Salmon Faverolle who is about 4 weeks old, we have 5 other girls who range from about 8-11 weeks old. We have read that putting the two new girls into the coop at night would be the easiest route to introducing them, but it seemed the next morning they would not accept our Salmon Faverolle, they didnt want to accept the Americana, but her being 6 months old and a lot bigger, the battle was given up on quickly.

We removed her from the flock and are keeping her inside a cage right now, we tried taking her out and introducing her again during play time while all of the girls are running around the yard, but one of our most friendly hen's (who we believe is at the top of the pecking order) instantly ran over to her, jumped on her back and tried pricking her little feathers out. I am very fearful of this happening again, so we have been taking her out with us, but her being in her cage around the other girls, but still the one hen is still very agressive at trying to get at her through the cage. We have been considering buying another hen around her age to keep her company, and then introducing them together when they both get bigger. Any thoughts would be great!