User blog comment:H. Mills/Caitlin Snow - Killer Frost???/@comment-106.69.153.200-20160116154617/@comment-4588264-20160116175453

From what it looks like, she'll most likely appear in the episode "Welcome to Earth-2", where they travel to earth-2 since there have already been numerous set/promotional photos of her. Or she could come sooner too, which I certainly hope!