I agree with you here. It's an interesting theory, but I honestly don't think AF would have killed off both Nicola's main antagonists - Lois and Marie. She works so hard at making the school books at least seem naturalistic (whatever may happen in the holidays) that I don't believe she would have put in two such similar deaths, in which the hated person just disappears, unmourned and almost unnoticed, from Kingscote society.