Disclaimer: I don’t intend this to upset anybody or bash anybody else’s headcanon. This is pretty anti-Mary, so if you want to avoid that, this won’t be up your alley. I’m not a medical professional and can’t give any sort of professional diagnosis. I can, however, give my opinions on what the writers and actors, who aren’t medical professionals either, could be going for.
I’ve had Mary on my mind lately, and I went back and re-watched HLV for any clues in her micro expressions as to what she’s really feeling (given that Amanda didn’t know about her background before, I didn’t think it’d be very useful to watch for clues in the other episodes. I will use bits of the dialogue from the earlier episodes though, since the writers knew). And the more I watched, the more questions started popping up. She’s by far the most enigmatic and divisive part of the show right now. But the one consistency that I saw was that her behavior is quite psychopathic.