-> can block AA (hard, when you dont know if he attacks creep or you)
-> high AS/AD/MS
-> ulti multiple on-hit (lifesteal!!)
-> cannot be targeted in ulti
-> gapcloser (with Q and R)
-> ulti can be canceled (will tell how in How to Counter)
-> no ranged harrass
-> low/average sustain w/o lifesteal (must buy at least vampiric)
How to Counter:
As I said the ulti can be canceled, you just need to block at least one hit so the AP carry should buy
, this will stop her ulti - dunno if it is an unfixed bug or just should work this way. If you play blind pick you may play fiora vs fiora, then you can block ulti with W-spell and use ulti when her w-spell is on cd ... but you dont read whole counterpick list when playing blind pick^^.
Another thing is, that Fiora is very vulnerable to cc, cause most times squishy build - you can healup almost save in ulti and heal yourself up with lifesteal when E is active - but if you stun/snare/exhaust/etc Fiora her dmgoutput is almost gone and so her lifesteal that you can burst her down. Sometimes Fiora will go very much Lifesteal, then make sure you have healreduce (Executioners calling if needed!).
Fiora deals almost only physical dmg (W spell deals 260 magic dmg when you block an AA) and most dmg applies on-hit effects (E gives +120% AS, ulti applies onhit effects). On-hit effects are not only more dmg or lifesteal, but also ninja tabi or thornmail, so if you have thornmail + ninja Tabi you almost have 200 Armor (67% dmg reduce) and another 10% lower dmg from AA/On-hit means more than 70% dmg reduce.
: dodge AA and high dmg with his stun, after Fiora's W
: AS slow, can stack armor for more dmg, slow, ranged harrass
: Fiora is very vulnerable to cc