The greatest champions globally to counter Kai'Sa include Naafiri, Nidalee, and Gragas. These are all great at countering Kai'Sa with decent win rates over 54%. Even if these Kai'Sa counter picks are not used in the same position as you, it's not smart to play her into one of these matchups. They will very likely beat Kai'Sa.
Conversely, if the enemy team choses either Galio or Rumble, you should seriously consider selecting her, as she easily wins against these champs with win rates over 56% against each ofthem.