I'm not sure if it's just me, but I basically never find a situation where I would prefer Jaina's sA to her fA.
fA starts just as fast (11 frames), has way better range, way better hitbox, leads to the same amount of damage, is throw invincible and can even anti air at certain ranges.
On the other hand, her sA has so little hit advantage that at some ranges the combo sAxxB will whiff, losing the point of damage and even leaving space for a smashed reversal to hit back.
Personally the only time I ever use her sA is by hitconfirming it as an OTG combo ender after a very late fA, which I'm not even sure was intended.
My suggestion would be to either make it faster and/or add hit advantage, or even better, give it the animation from her attack card in Yomi. With this last suggestion she could use the normal to fake Bs and bait jumps, and it would not only synergize with her kit, but also help in the Geiger MU (her worst) to bait Supers.
Now, I understand that she doesn't really need a buff, but with a game with so few moves it would be best not to have any useless ones.
That said, if some of you guys actually know a good use for the move, then forget I said anything.