Unlike Superman who is Clark Kent, or Bruce Wayne who is Batman, in case of Caitlin Snow / Killer Frost they were more like two different personalities and characters.
They were basically the same actress that just changes when Killer Frost takes over, but in season 7 of The Flash they literally separate into two separate people so they can be onscreen both at the same time.
So, for example in 7x07 of The Flash... https://www.tvmaze.com/episodes/2062318/the-flash-7x07-growing-pains
We have Danielle Panabaker credited as single character Caitlin Snow / Killer Frost even though they were always "two", but by now they are split so the human scientist Caitlin Snow and metahuman Killer Frost should appear as two separate characters.
Sort of how in DC's Legends of Tomorrow Jefferson "Jax" Jackson / Firestorm and Professor Martin Stein / Firestorm are two separate characters that can merge into single new one called Firestorm. Here Caitlin Snow and Killer Frost should be split now. The only problem is to decide where and when to split them. Seeing how they split physically in season 7, perhaps from episode where they split we could have Caitlin Snow and Killer Frost characters as separate portrayed by same actress, and the past Caitlin Snow / Killer Frost can remain like that for episodes before that... or if in the future they become one again that can be reused.
If we would split them throughout all seasons, we'd have to keep track when Killer Frost took over Caitlin's body to know under which episode to credit that character, although that would probably be more correct option but would require a little more work (or maybe less, since current one would just be renamed to Caitlin Snow and new one would be added as Killer Frost and attached to episodes she appears in).
So, any idea for how this would best be done, because as things are right now (at least in episode 7x07 I last watched) they are physically two separate characters.



