These 2 tips will help you beat fiora.

If she misses Q early game, it goes on a 12 second cooldown and thats her main form of damage. Her W is very strong but is also on a extremely long cooldown. Once she uses it you can pretty much burst her for free if she goes for some cs.

Late game if you have she is very easy to kill as a champion like cause you basically remove her lifesteal.