Buffing Fiora's stats or scaling won't help
She has the damage, mobility etc. To do well.
IF it was possible to land all the vitals on her ult. Its just not realistic that you'll land all of the auto's, it takes to much time and in the end, almost 100% of the time you'll probably die in a team fight before you even get 3 off. As its much to time consuming to walk around and auto. You'd be better off just not even trying to land them, but instead just auto'ing their face instead of walking around them trying to hit vitals.
Unless you make those vitals do like 20% of there health each. Its almost never really worth it to take the time to hit them. And its next to impossible to hit them anyways in a fight.