I'm not so sure if Dahye was ever a hero tho
Considering how she acted in the later arcs in part 1, she spearheaded attempts to get justice for what happened to her despite she herself being the reason it all began. It's how I interpreted it.
That's true, but I would say that her reasons to "make a right thing" were rather selfish and she only wanted to get a revenge on Yeonhwa (which is understandable, except that she also did a lot of messed up things). I also though that she was getting a sort of a redemption arc in the end, when she was helping Yeonhwa's little sister and at that time she was actually acting like a hero, but then the ending happened and it got revealed why she even cared about this girl in a first place. Idk, I've always seen her more as an antagonist - not necessary a villain, but also not a hero, tho that's just my personal pov. Which is why I'm really curious about this sequel, cause it looks like Dahye is more of a bad guy there, although I'm not 100% on Yeonhwa being able to have a normal life and she may be intrigued by Dahye as well. Just doubt that this will be a standard villain-victim dynamic
So fascinating how the tables have turned this time around. I feel like Harvey Dent's quote best sums up Dahye right now: You either die a hero or you live long enough to see yourself become the villain.