Sorry you had to experience that. "Homicidal hen" is the same term I used for one of my buff orpingtons. I tried to foster chicks to her and she brutally attacked them. She was so focused on setting that the hormones never switched over to "tend the chicks". Instead, she was totally focused on "defend the eggs". When I let her try to hatch eggs, she continued setting and actually crushed the chicks that were trying to hatch. She's on the short list for chicken soup.
After decades of being produced in industrial hatcheries, many hens have simply forgotten the ancient wisdom of setting, brooding, teaching, protecting and mothering chicks. Sometimes they get part of it right, but it takes the full suite of skills to successfully raise chicks. Fortunately, I've had good experiences with two broody hens this summer. Both have been very good moms, and I have a much greater appreciation for their skills after witnessing the actions of the homicidal hen.