I was asked to bring in a second opinion so here I am.
I agree that the move's description made it sound like the move waited until Shayda was hit; however, it seems to me like Shayda should've blocked the attack. When we take a closer look, ya see:
Whenever an oncoming projectile attack is aimed at her,
Yep. Oncoming, meaning she uses the move in the space between the time the attack is used and the time it hits.
My four haypennies for ya.