I think a person doesn't suddenly get to a place in their life where they feel nothing for killing family members or inflicting cruelty and pain, even feeling happiness when they are lying dead in front of them, having no humanity. I think it makes more sense that the person was always that way, disconnected, without empathy or humanity, capable of inflicting the worst of the worst cruelty upon others, and the times when others saw them differently they were just manipulating them for gain, for the love they would get. I think she's probably always been a psychopath and a narcissist and it's the only answer, as to why.