Story idea

A villainess isekai story, but, rather than being a fan of whatever game who has been reborn into its world, the main character has no memories of her past life and stumbles on a comprehensive walkthrough for the game. How did it get there? Who knows! It's there now, though, and after reading through it and finding out that she's in for a bad time on every route, the villainess is determined to change her fate by ...changing her behavior.

It can't be that hard, can it? All she has to do is the opposite of everything she does in this "game" thing. Even if the decisions that other her made did all make total rational sense, and she has no idea why anyone would blame her for them.