If Amelia is laying eggs, she is over being broody. I have a hen and a chick now about that same age, and the chick roosts with the flock, next to the hen. But it is more of a tolerance, not a mother daughter bond.
4x8 = 32 feet - so enough space for 3 adult birds. As the chicks grow, they take up more space, and I would expect in that 4 x 8 space, there is no way for birds to get away from each other.
I do think there is a strong possibility of wreck when you go to add the hen and pullet to the flock. Unless, they have been in sight of the flock, they are going to be complete strangers to the flock, and will be attacked. At this stage the hen will not protect the chick, she will be busy protecting herself.
I do it differently. I hatch out in the flock. The broody hormones are highest, making the broody hen powerful. She introduces the chicks to the flock, and will protect them. Mine take the chicks out of the nest at day 2. The chicks grow up in the flock, and when the mama forgets them, they have been accepted into the flock.
Mrs K