Just curious, have you seen a feral rooster or any other feral chickens hanging around?
Personally I would be tempted to adopt her and give her a safe place to raise her chicks. Depending on your predator load, just because predators haven't got them yet doesn't mean it won't happen. My only concern would be whether or not mama hen carries any diseases. Chickens carry many diseases for life and will infect other chickens even if the carrier birds seem healthy. Mareks Disease, Lymphoid Leukosis, Mycoplasma Gallisepticum and Synovae and Coryza are only a few diseases will infect birds for life if they are exposed.
Again, even knowing the risks, I would personally be very tempted to adopt the family. One, because I have a soft-spot for mama hens, and two, due to the high predator load in my area, homeless chickens would be lucky to survive their first night in the wild. Know your risks, and make the decision you think is best for you and your current flock.