Not if you build armor. Playing as a tank with a weak early game and no ranged csing abilities is absolute torture versus Fiora.
I know it's a hard counter, but sometimes you get counterpicked -- playing Nasus into Fiora is balls. It is stupid. At no point in the game and with no strategy can you beat Fiora 1v1 and you will never get enough farm to contribute elsewhere on the map (if she is any good). Even if the jungler ganks for you and gets you ahead it doesn't matter.
She is a severe lane bully early. She can use her mobility to zone you away from all creeps. You will get few stacks. Normally in these situations as Nasus you want to stack armor and play for the later game (It's easy to win versus a pantheon and with good decision making you can beat a riven). But her % max health true damage means that doesn't work. She can kill you almost as quickly regardless the armor (or health) you build. The only way to win a fight with her is to kill her faster than she kills you. But because you can't get stacks and because Nasus does his damage over a more extended time, she can out-heal your damage.
It's so stupid. I remember build a good amount of armor versus Fiora and a large majority of her damage would be %maxhealthtruedamage.
Sure counterpicks happen but Fiora has no weakness in lane. Gating her mana, as OP suggests, would give me counterplay. I could bait out her mobility or parry spells, giving me windows to farm q. I can't do that as things currently stand. There is no way to win lane versus a competent Fiora as Nasus barring the jungler camping top so that I can get a hefty lead on her, and let's be honest that shouldn't be necessary for a matchup not to end in utter disaster.