she will more then defend them, believe me, she is better off with the girls so you do not have to reintroduce her,and the little ones at a later date. I learned this the hard way, it took months and months to reintroduce those chicks/ pullets. And mama got picked on something awful . I have raised 3 sets of chicks now with a broody, they know how to care for there babies and will do a great job introducing them to the flock and letting the flock know to stay clear. I let my girls out in my yard with the babies after only 3 days, she teaches them right away what to eat, how to forage etc. it's adorable. And the other hens who go near her chicks will get a peck and a chase away. If possible, alwYs leave mama and babies with the flock.

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