So last week a script came out for Episode 7 For Season 3 Of the Flash and the pages were in the shade so you can see though the pages and people saw the words killer frost so obviously she is going to be in the episode so these are possible ways that she can come back
If flashpoint is still going on towards episode 7 then it is possible that we can see flashpoint Caitlin become killer Frost
2.Another Version Of Killer Frost
It Is Possibe We can see another version of killer frost like the "Louise Lincoln" Verison, However it is not guaranteed
3.Killer Frost In Earth 2 Is Still Alive?
Somehow or someway it is possible that killer frost that we saw die could still be alive or maybe just resurrected
4.Earth 1 Caitlin Becomes Killer Frost
So Now this is where it gets weird Caitlin from earth 1 could have been affected by the PA or maybe he Metahumen Gene has not been awakened yet