Seeing that she can actually show something other than calmness or silent pleasure on her face completely destroyes the image of her being pure evil. And she's crying when she is throwing her hairbrush at the mirage-reflection of Ursa. I don't thinks it's remorce, I think it's just frustration. In fact, the pictures that show her anti-calmness all look like that she is frustrated. It could be that what most people think, that she is frustrated because she became a Fire Lord with no power and a war to take care of. But now the constant family instabilities and her insane state of mind could mix with that frustration and create an inbalance in her persona, which would cause even more frustration. She might find that she won't be able to produce lightning anymore...
You see what I'm saying? I'm not really good with words so it's kinda hard for me to expain completely. There is alot more I would say if I knew how to say it...