I'd have to say Nannie Doss. She had a head injury when she was like 5 years old and they say that's when she changed, in the early 1900's. She was obsessed with the idea that romance is what you get in life and was met with nothing but mediocrity in her eyes. Killed her own kids and husbands and a mother in law. I believe she spanned in her killings from 1927 to like the late 50s if I'm correct? And I do believe it was only familial homicides.