Devil's advocate: Was she really all that kind before? Who actually says this? If it's NPCs, I'd just say they're naive about their leader. If it's Garnet, she might be naive about her mother from such a young age.

What I'm saying is that I actually don't think it's very much of a stretch to say that the 'she used to be so nice' is a clouded judgment from whoever made it and something the player should be skeptical about.