The best champs out of lane to counter Fiora include Zeri, Caitlyn, and Kalista. These champions are all great at countering Fiora with win rates over 56%. Even if these Fiora counter picks are not chosen opposite your position, it's not a good idea to take her into these matchups. They will most often beat Fiora.
Yet, if the opposite team choses either Skarner or Kennen, you should strongly think about taking her, as she easily crushes these champions with win rates over 53% against both ofthem.