You're just bad. I'm sorry, but it's true. League isn't team death match and different champions have different strengths and weaknesses. Rivens strength is specifically laning against low range opponents. You can choose to pick low range champions who have weaker early game's then rivens and try to fight her and die over and over like a noob, or do literally anything else and have a reasonable chance to win the game.
Things like playing passive and outscaling her, taking a champion who bullies her from range (kennen, quin come to mind), picking a similarly strong laning top champion (old darius, renekton, pantheon, etc), picking a safe farming champ and teleporting around the map to make plays, controlling the minion wave to freeze at your tower, buying some fucking defence, all come to mind just off the top of my head.
That doesn't even get into raw mechanics like how to trade well as any given champ since you've already established that you only like to fight to the death all day, but assuming you learned that you could take armor and potions and with good trades outsustain her and force to to go back to base and heal which gives you a level and gold advantage and maybe even some damage on her tower.
...or you could rush to lane to all in her every 10 seconds and die and make threads about how op she is.