The top picks not in lane to counter Fiora include Zeri, Caitlyn, and Kalista. These champions are all good at countering Fiora with high win rates over 56%. Even if these Fiora counter picks are not taken opposite your position, it's not smart to play her into any of these matchups. They will usually win against Fiora.
Yet, if the opposing team choses either Skarner or Kennen, Fiora mains should strongly think about picking her, as she easily destroys these champs with win rates over 53% against both ofthem.