The greatest champions out of lane to counter 세주아니 include 칼리스타, 드레이븐, and 케이틀린. These champs are all good at countering 세주아니 with decent win rates over 61%. Even if these 세주아니 counter picks are not picked in the same position as you, it's not a good idea to play her into any of these matchups. They will usually win against 세주아니.
Yet, if the other team picks either 갈리오 or 스웨인, 세주아니 mains should strongly think about taking her, as she easily beats these champs with win rates over 52% against both ofthem.