The big reveals start after the battle for the Elf Village from Kumoko's point of view at Chapter 301. It's after the Past Arc and it's still an ongoing reveal.
From a standard point of view, Kumoko was never a good person to begin with. She was all about enticing adventurers to attack her so that she could collect their XP (and meat) in "self defense", and she's a huge fan of elf genocide. The author even calls her the Primary Perpetrator of the present, being the architect of the Human-Demon Great War, the reason for all of Shun's misery, and basically the mastermind of most of the messes in the present time.
That said, she's also the person working the hardest to save the world, and she's making up for the neglect (or active harm) of the other Administrators. It's just that her methods usually involve the mass slaughtering of people.