I'm not sure how Evvie would have been able to spread her wings and fly with the water blade heading straight for her back as it would collide with her wings even faster than her spine. It is moving slower, but it's still moving very quickly, arguably faster than Evvie can notice her staff defence has failed and bounce back into the air.

It also wouldn't be holding onto her staff at all, as you mention it encumbering her. Though that could have been a possible attack it's not what I went for.