Just feed the non medicated starter to everyone. Keep a separate bowl of oyster shells out. I don't use layer anymore as I find it doesn't have enough protein to support backyard flocks where extra stuff is feed. I feed an All Flock and a non medicated chick starter. They will eat more oyster...
Very cute chicks in a feeder. I get them out there very young too, size of the set up and how confined seems to be the big determination of whether it's going to go quick or not. My birds have lots of room and lots of places for chicks to get away.
A single bird being integrated can take longer than a group. I would expect weeks, and maybe a month or two before she's part of the flock. Keep her separated when you can't watch until so they don't peck her too much which will set everything back.
It normal for the younger ones to stay away from the adults, it will be a year or so before everyone freely mingles. The young ones will stay in there own group more or less for the rest of their lives. They are young and the young run, make sure they have places outside to hide, something to go...
Just integrated my 4-5 week old chicks. Had them penned for about 5 days, opened the door yesterday. They are out and about like they own the place. An occasional peck but nothing serious, one was trying to take food out of an older hens mouth, another was pecking at my oldest roosters wattles...