Oh yeah, she has Mad Queen written all over her, but I don't know if she fell over that edge just before or just after Tommen's death.
edit: Although I guess technically blowing up the Sept indicates just before. But there might have still been a little left? I don't know where I was going with this.
She's off the deep end either way, so the end result may be the same. But I love pondering her character evolution during those last few episodes.
I guess the biggest question you have to ask is...was Cersei's intention to take the throne, or was she just trying to eliminate what she perceived as a threat to her family? It seems like a tiny distinction but it makes such a big difference overall.
In one instance, you have a mother going to great lengths to protect her son. Ultimately failing, despite her best efforts. His death severing that last little bit of restraint and maybe even sanity. It paints the picture of someone who is primarily driven by some sense of grief and loss.
In the other, you have a woman who has been systematically fucked over to the point that she can't stand it any more. She's driven by anger at EVERYONE, including her son, because she realizes that even her son has turned on her. So she made the choice to eliminate ALL of her perceived enemies and take power for herself.
I'm kind of leaning towards the latter of the two. When she climbs those stairs and sits on that throne, I didn't get the impression that she was surprised to find herself there. I felt like THAT was her plan from the start. I don't think her plan was "Get rid of obnoxious dirty sparrow people, then my son will listen to me and love me again." It felt like the throne was her goal all along.