Although there are definitely flaws with the theory, Killer Frost obviously knew Ronnie quite well back when she was Caitlin Snow, and we’ve already seen over on Earth-2 that an evil Caitlin and an evil Ronnie make for formidable pair of baddies.
Now, judging by Danielle Panabaker’s tease to EW, we can safely say that Killer Frost knows Savitar quite well.
In fact, her words lend even more credence to the theory that none other than Ronnie Raymond is Savitar.
There have been plenty of candidates for the man in the Savitar armor throughout Season 3, and the only one we’ve really been able to rule out definitively is Hunter Zolomon thanks to actor Teddy Sears’ recent remarks.