If we had to nerf Fiora, i would take a look at her mana costs.

From the games I've watched and played, Fiora's mana costs are pretty damn low. All at level 1, Q has 20, W has 50, and E has 40, with the staple 100 mana for R.

Those are pretty damn low, for the mobility and utility they serve in proc'ing her passives. I would take a look there, IF Fiora proves to be too strong. Emphasis on IF