Board Thread:The Flash discussions/@comment-4036559-20181121182754/@comment-27700324-20181126215243

Seems it just took a while to really activate those genes considering she wasn't aware of it. Just like how DeVoe kept Killer Frost in a deep corner of her brain, Caitlin herself did by simply not being aware of it. Then after the kidnappings from Zoom along with Barry's changing of the timeline making herself fearful that something might have happened to her, it had her brain activate those genes in a fearful manner. Making Killer Frost evil instead of what we saw this season and in season 4 which was a good Killer Frost.