Actress Danielle Panabaker expresses hope for the upcoming Season 4 of The Flash to explore the story of Killer Frost and the motivation for being evil. Panabaker said:
One of the things I wanted explained last season that I don’t know was ever totally clear, and I don’t know that we have the answer yet, is why Killer Frost is evil. I’m not totally sure why everything she does causes the physical body of Caitlin Snow to act so badly. So I’d like to know a little bit more about her motivation and why.
Source: Comic Book