Well that's not really true. Cersei destroyed a building with wildfire. A building full of her enemies that wanted her dead is no city full of innocents.
She didn't just kill her enemies, though, that room was full of innocent people, their uncle and the explosion seemed to destroy multiple buildings surrounding the main building. Cersei probably killed hundreds of innocents.
Don't worry I got you:
https://www.youtube.com/watch?v=KFELQv3yWFI
She loved him, cared for him, and he treated her like shit. All of it shown in one small clip.
Yeah, I brought up that scene in another post.
Then later we see him being murdered in front of her and she does nothing or seems to really show any emotion towards what just happened.