Q (if she doesn't hit any target): 13-6
Q (if she hits a target ): 6.5-3
Fiora's Skill Max Order: Q → E → W
Build Advice: Rush Berserker boots as your first item against Fiora. You should start with doran's, then use your next 1100 gold for these boots. Movement speed renders Fiora useless and it will tilt her insanely hard because you never need to use your E to run away from her engage.
Level 1: Fiora will start Q 9 times out of 10, but be careful for the odd fiora that might start W to counter your level 1 vault. If she starts Q, let her Q you and then vault her mid Q, you will cancel the dash and then you can run her down with autos. Her Q will refund 50% if she hits you, so be cautious of this. Vault her Q, and you have 6.5 seconds to get a few autos off before running away. Do a short trade, then back off after around 4 seconds from her using Q. Don't be too greedy with autos because her Q comes up before your E does. Be cautious of her vital passive. It will mark you and highlight the vital area, meaning if she hits you on that angle she does bonus damage. What I like to do is if a vital spawns that's easy for her to hit (the vital is on the front side of your body) then walk in a bush OR out of vision, and the vital will reset automatically. This tip will help you a lot in lane to prevent fiora from getting good vitals.
Level 2: Now Fiora has W. Do not use E aggressively because her biggest win condition in lane is parrying your vault to stun you. But, with celerity + nimbus, you are faster than fiora, so you don't even need to use E that much.
Pro Tip: What I like to do to beat Fiora W is when she isn't expecting it, I vault her randomly and then INSTANTLY side step, before even autoing her. Clip Here Do this extremely fast. Fiora will always W instantly after this vault, but if you sidestep quick enough, you miss her W entirely, and then you can attack her to consume the harrier mark to then run her down. This takes practice, but if you master it you can do it against every Fiora player. Quinn's E animation is too fast for Fiora to react to, especially if you do it at an unexpected time. Her W is 24 second CD, so making her use it gives you a big window to take good trades afterwards.
Level 3-5: Fiora Has E, but the matchup is still the same. If she Qs in for a minion or tries to engage on you, Q her and auto to consume harrier, and use W movespeed to run away, you will out run her without needing to ever use E! Ignite her if you feel like you will die because it gives you nimbus cloack speed.
Level 6: Fiora's R gives her MS, but your W passive makes you quicker, so it isn't a problem. When she Rs you, I like to ignite her to get nimbus speed to counter her R; otherwise, Q her and auto the harrier mark. With W max, this should be enough to out run her trying to engage on you without even needing your E. This is why I prefer boots rush in this matchup because her only win condition is countered with movement speed. If you are going to die, blind fiora THEN E her while blinded so that she can't see you using vault as a last resort if you need to use your E.
Level 1 Fiora will start Q 99% of the time, and if she uses Q on minion or you, trade with your AA - Vault - AA combo immediately.
If she Qs the minions level 1, her Q is a 6.5 second CD, so your vault will come up after her Q returns.
If she Qs you, vault away and trade because that's all she can do.
Be cautious after though because her Q will be up about 3 seconds before your vault cooldown comes back up if she hits you with it.
Level 2 onwards is where you must be careful.
DO NOT USE VAULT OFFENSIVELY after level 2 fiora because she will use her W- Riposte and you will be stunned from your vault, which often leads to death.
The only time you should use E offensively is if you do it when she doesn't expect it.
If you E aggressively, instantly walk side ways because Fiora will Q+W forward, but if you side step quicker, you will dodge her W entirely, which is huge for the matchup.
Essentially, with W max, you should be able to maintain distance from fiora indefinitely to the point where Fiora is FORCED to use her W- Riposte offensively on you as a slow to engage on you, which means she should never be able to stun you with it.
When she uses W offensively, immediately follow with Vault + harrier auto attack to push you to safety and grant you movement speed from your passive to outrun her.
Your Attack speed will be slowed if she hits you with her W- Riposte, so just be cautious of that since it will likely make you cancel your AAs if you don't know about that part in Fiora's W.
After level 6, whenever Fiora presses R on you, you can use ignite + nimbus for speed.