i think the darkness that you saw was her selfishness, and that selfishnes manifested itself into badness and evil as it tends to do in life
i also felt sorry for her but also very frustrated.
I have argued mia being selfish, because some people state she was not being selfish but doing it all for her chap. But i stand by the fact that i think she was very selfish as she gave no thought to the chap at all (which would have saved everyone a lot of bother if she had)