Originally Posted by
boost
I don't think she had a plan all along. I think that as the reality that power was slipping away from her became more and more real, she stopped trying to play the game and reverted back to the spoiled brat she grew up to be. She knows how the game is played, she knows the unwritten rules, she admires her father greatly for his ability to play the game-- but deep down, she just doesn't have what it takes, she grew up with no struggle. She doesn't have the patience to play by the loose rules everyone else is adhering to, and it's obvious to all the other players, which makes it obvious that as soon as there's a short term gain to be had by betraying them, she will. So they don't play with her, and this makes her even less patient. We saw in e09 (?) her last ditch effort to play the game when she approaches Olenna.
Cersei is the story of a child trying to fill the shoes of their exceptional parent. But due to her blind admiration, she wasn't able to parse the examples her father made-- she couldn't get the most out of his tutelage by examining the man with a critical eye, so she becomes an exaggeration of all of his worst qualities with none of the good.
She wasn't planning this, she was keeping it in her back pocket out of fear that she'd fail to be half the player Tywin was, and in the final episodes of this season that realization came to fruition.