Eh maybe that's why she's on that list. I suppose Captain Cold is on it as well...
How many hints do we really have at Killer Frost though? Other than Cold Girl in the crossword and everyone going crazy bout that cheevo picture?
Hmm, aside from the crossword and the achievement pic, the only other hint I could think of was that one tweet from Boon (though it could just be Boon's typical joking behavior)
https://twitter.com/noobde/statuses/307925240489574400
RT FrogLantern @noobde I have been eagerly anticipating Captain Cold. These Killer Frost rumors make me sad. EB: Stay Frosty! #Hicks
From the original debut trailer for Injustice, we know there is at least one character who uses ice beams (the one shooting Flash). If the roster for Injustice really is only 24 characters, and if 3 out of the final 4 character slots are really gonna be Black Adam, Ares, and Raven, then that 4th and final slot (who would be the mystery woman from the achievement picture) just has to be the ice user.
However it's entirely possible that the roster is greater than 24 characters, and maybe Captain Cold was the ice character shooting at Flash, and maybe the the mystery female in the center of the achievement pic is some pale redesigned version of hooded Circe. We'll see.