It depends on your coop/run situation. In the run, you need places and obstacles where the mama hen can defend her chicks. My mama hens would put themselves between the babies and the other chickens. Many of the pictures of the runs I see on here are just one big space, with no roosts, or shelters, or boxes in them. If you add stuff like that, it allows any chicken a place to get away from the others. It looks more crowded, but it actually multiplies space at different levels. Plus gives a bit of interest and exercise to the girls.
I kept mine with the flock, and it worked well for me, but my mama hen was tough with the other hens, and I had them free ranging most of the day. I have a pretty small coop, so just placed a box on the ground on its side, under the roost, put some hay in there, and she would take the babies in before dark. The layers roosted above her.
As they have gotten older, they do get a few more pecks from the other hens, but have learned to stay out of reach for the most part. I do offer a couple of places to feed. When they free range, for the most part, they stay together as one flock, with a little separation within the flock.
There seems to be many posts on here about reintroduction issues, and I am glad that I avoided that. With only one chick, it might be best to have it with the flock as soon as possible, but it will depend on the mama.