The same way you could almost hear Tom Haverford saying, "Turns out, she was crazy," about Daenerys, the same reductive sentiment seemed to guide the writers in Cersei's final motivations. The only motivation we're given for anything Cersei does in the final season is her unborn child, but not exactly why. Her hubris maybe drives her to push Daenerys to the edge, but wouldn't treading that close to danger be more indicative of someone who has nothing to lose, not someone desperately trying to survive?
Cersei's legacy is that she became the best and most insidious villain this show had ever given us. And this show had always given its awful villains the most deserving deaths: Joffrey is poisoned until he's purple, Walder Frey unknowingly eats his sons, Ramsay is frickin' eaten by dogs.
But Cersei? She dies in the arms of the one she loves most. Her being crushed is almost peaceful compared to the revenge other characters have inflicted. I know it sounds counter-intuitive to champion a female character's death while being enraged at their treatment, but what I'm saying is that Lena Headey, the performer, deserved a more poignant death scene.