Board Thread:General Discussion/@comment-6192846-20151223075113/@comment-6986530-20151224052744

Everything else aside about how much of a "broken teenage girl with a terrible life" that Margy was, it's pretty explicit that Margarita's craziness was a result of having Eve lurking under her psyche. There's also, on the opposite side, nothing stating the Venom is the reason that Eve went crazy--in fact, Eve's mental state by Gift is more attributed to her long body-swapping life and the overall state of her soul.

On another note, Kayo's insanity of attaching her child or husband to whoever at hand is close enough might explain how, each time she sees Kai, she assumes he's her husband--if she decides that her husband is a man with a burn scar.