User blog comment:Sachoras/Cersei - friend or foe?/@comment-5014364-20121221033022/@comment-5894352-20121222164007

I think there's more to her than you give her credit for. It's not as simple as "Cersei is bad". I think she actually sees a fair bit of herself in Sansa (remembering how she was hopelessly in love with Robert at one time) which she now resents as an old weakness in herself. She doesn't want to see Sansa make the same mistakes she did of simply "going through the motions" of loving her king. I also think she did show some appreciation at that point that her son is a terrible human being.

I think she let her guard down briefly in A Man Without Honor showing a glimpse of her human side. But by Blackwater, she put her armour back on.