What can a man do for a corrupted woman?

Elsewhere on the internet, a caring father of an early 20's girl who had recently taken a noticeably sharp turn towards acting like the standard self-hating women asked to hear thoughts and suggestions about what to do.
This is my best attempt, and while it isn't a bunch of good news and easy steps, it does provide some immediately actionable advice and explicitly acknowledge that if a man can just keep a woman from getting any worse than he's performed a miracle.