History is replete with examples of people who conspire against family members to gain power. One extreme example: Byzantine (Roman) empress Irene, who had her son blinded so she could 'succeed' him in to power. The blinding was poorly done, and eventually led to his death. Not enough information exists to know if the blinding was done badly (with death made probable) intentionally or not. Byzantines liked punishment like maiming because it stayed clear of the 'Shall not kill' commandment.
Generally speaking, people who are capable of things like matricide (Katherine) need some degree of mental damage to get past the mental framework that's more common among Homo Sapiens.
Armchair psychology: (I don't play one on TV because they havent asked):
I don't think she's a narcissist. Ruthless to the point where she's able to cause any amount of harm to people, regardless of her relationship with them. And from birth, she would've known that unless 'something' changes, she was never getting the throne herself. So she changed something. In honestly a rather poorly thought out fashion. Smarter would've been if she wiped out all competition, smarter still if she did it in some ambiguous fashion, or at least in a way that's easily pinned on a traditional enemy.
So I'm leaning more towards sociopathy, as she's generally well in control of reality and rarely warps it in her favor to the extent a narcissist does.
But she clearly lacks the ability to feel empathy, lies frequently, and doesn't plan things out as well as would be prudent, if just from a self-preservation perspective.
