Cersei understands the consequences of her absence and she is absent anyway, which means she does not intend to suffer those consequences
I've had lots of time to think about how good I was at seeming good
I killed your High Sparrow and all his little sparrows. All his septons, all his septas, all his filthy soldiers, because it felt good to watch them burn
It felt good to imagine their shock and their pain. No thought has ever given me greater joy.