The top champs out of lane to counter Tristana include Naafiri, Nidalee, and Sylas. These are all great at countering Tristana with win rates over 56%. Even if these Tristana counter picks are not chosen in the same position as you, it's not a good idea to take her into any of these matchups. They will very likely win against Tristana.
Yet, if the opposing team brings either Shyvana or Maokai, Tristana mains should strongly think about taking her, as she easily destroys these champs with win rates over 53% against each ofthem.