BUFFY THE VAMPIRE SLAYER GAVE US THE BEST DARK PHOENIX ADAPTATION OF ALLQuote
After being the quote-unquote "good girl" of the group for years, a young woman comes into her own by both discovering new powers and also undergoing a sexual awakening that stops her from simply being a damsel in distress and the object of desire for the men in her life.
Over the course of time, she develops her powers. But eventually, she becomes addicted to these powers and is slowly corrupted by them.
Then, when tragedy strikes and a minor adversary kills the love of her life, she's consumed by rage, brutally destroys said enemy, then temporarily loses her humanity to become a nigh-unstoppable villain who fights and overpowers her friends with designs to destroy a planet. But before she can, another longtime friend confronts her, and manages to remind her of her humanity, which she manages to regain before it's too late.
https://www.google.com/amp/s/www.syfy.com/syfywire/buffy-the-vampire-slayer-gave-us-the-best-dark-phoenix-adaptation-of-all%3fampThis mess had been brewing for seasons and the audience knew sis was growing more and more powerful and using darker magic.
Game of Thrones should have also referenced this if they wanted a convincing decline for Dany into madness.
