she needs something that helps her not to get shut down by cc while trying to trigger those 4 passives on a moving target instead.
It's going to be defense with a bruiser build-path :/
She's going to go in the Aatrox/Irelia/Xin route of a light fighter turned heavy. Her AA steroid obliterated crit scaling, true-damage on multiple skills removes armor pen as a major scaling factor, and %max HP true damage is going to let her deal meaningful damage as a tank. Sounds like the scaling is high - but same case with Darius. Why go glass when you can be a tanky juggernaut that can survive long enough to apply 5 stacks and actually use re-sets?
On an old-fiora build? Yeah, target would need to be a potato for her to get her ult off.
On a Mundo build or at least Irelia build? She'll probably be able to get 3 of the 4 in a team-fight, especially if she goes Trundle status and just targets a tank/bruiser to make them think twice about moving out ahead.
Really do not see glass-cannon working on her anymore. From what you said people will probably Q_Q about a glass-Fiora beating the snot out of the type of teams a glass-Darius, Xin, or Aatrox can annihilate. But competativly? She'll probably act more as a battle-cleric or paladin, focusing a little more on the heal, stunning people with Riposte, and laying down some respectable, armor-crushing hammer thwacks over anything else.
I don't see her not working - I just see her working in a way that's heavily divergent from pre-rework Fiora and working in a way that feels like a totally different champion :/