I would keep my eye on the situation, and not even separate her and the chicks from the rest of the flock. Obviously, if she abandons them in favor of sleeping in the tree, you'll have to intervene. But, the best way to integrate chicks is to do it right from the start. If Mama is a good Mama, she will kick the tar out of any one who messes with her babies. It might be a good idea to offer them some starter for a few weeks until they are big enough to eat the whole grains.
