Do not use chicken wire! Chicks can fit through the holes and will squeeze through, but may not know how to get back in and will be stuck on the wrong side of the divider, away from the hen. Happened to me. If you use a divider, go for 1/2” hardware cloth instead.
Whether the chicks will be okay with the flock depends on the other chickens’ temperaments, too, not just the broody’s pecking order. I have a broody with the flock right now, chicks are 3 weeks old. I had a chicken wire partition down the middle of the coop for lockdown and up to day 3 after hatch. When that chick slipped through, I decided to take down the partition and let them mix with the flock. My broody is low ranking and second smallest in the flock, but the mommy hormones gave her courage and she plucked a lot of feathers the first few days. My flock is very easy going and peaceful though, the hens all get along and they accepted the babies without problems. They kept away from them and their crazy mom for the first few days, but by now everybody has chilled out and now they all eat and nap together with no issue. I have everybody on medicated chick starter so I don’t care if they share meals.
Whether the chicks will be okay with the flock depends on the other chickens’ temperaments, too, not just the broody’s pecking order. I have a broody with the flock right now, chicks are 3 weeks old. I had a chicken wire partition down the middle of the coop for lockdown and up to day 3 after hatch. When that chick slipped through, I decided to take down the partition and let them mix with the flock. My broody is low ranking and second smallest in the flock, but the mommy hormones gave her courage and she plucked a lot of feathers the first few days. My flock is very easy going and peaceful though, the hens all get along and they accepted the babies without problems. They kept away from them and their crazy mom for the first few days, but by now everybody has chilled out and now they all eat and nap together with no issue. I have everybody on medicated chick starter so I don’t care if they share meals.