A description Episode 20 of Season 3 – titled “I Know Who You Are” – indicates that Killer Frost will be actively working against Team Flash.
Cisco will have a hard time working himself up to fighting against her, but I think we can guess what will happen if Cisco has to choose between protecting Killer Frost and protecting the lives of innocent civilians.
The good guys will be trying to work with newcomer Tracy Brand (played by Anne Dudek of House fame) to stop Savitar, but Killer Frost will be chasing Tracy for her own ends.
I’m sensing a major showdown happening by the end of the episode.