Comeuppance, why? Hasn't she suffered plenty? Think about what she's had to endure. She lost her mother tragically as a child, the circumstances of which caused her to develop a deep seeded hatred for the baby her mother died having. Being raised motherless by stern father who didn't love his children the way children want & need to be loved no doubt contributed to her forging an unnaturally close bond with her twin brother. A relationship that would grow more and more perverse until culminating with said twin brother raping Cersei at the foot of their dead bastard son's corpse....but that's jumping ahead.
It's important to note that in this world a high born woman's only real value is as a potential wife & mother. But when Cersei is offered to the Targaryens as a bride for Prince Rhaegar, the Mad King rejects the notion so harshly that Tywin resigns as Hand after two decades and rides home. After the war, she is deemed good enough by King Robert, a sad drunken man who was so hopelessly in love with a dead woman that he was incapable of loving his new wife. Still, she gave him an heir, a true heir, a beautiful black haired baby boy. But as if to cement her and Robert's doomed, loveless, marriage, their baby died. She lost her first born, and years later would lose her second. Even now, despite all the burden she bears, she's been forced into yet another ill-fated arrangement, this time with a gay man.
She's ruthless, greedy and manipulative sure, but wouldn't you expect that so much time in a harsh environments under extreme conditions would erode the positive aspects of a person and leave them cold and hardened? Cersei is one of the most sympathetic characters on the show. People only hate her because she's pitted against(and crushes) beloved characters.
