If Caitlin let Killer Frost loose one some random person, possibly killing them, then I would bet all my money on the elder Snow generation genetically or mentally manipulating the young girl into forgetting it, and then stopping her from being able to automatically conjure her icy personality.
How did Caitlin lose her Killer Frost powers?
Considering how little we know about this family, it’s also entirely possible that Killer Frost lived up to her yet-to-be-conceived name by being responsible for the death of Caitlin’s father.
Also a hard one to pinpoint for now, since we have no idea what happened after the crash.