She didn't have much time to react. She was the opposite of fire, the thing that could extinguish it. But he was attacking her and when that happened, she didn't have time to react to the other attack. Not when there was fire coming at her that could kill her, or at least hurt her. Again, she had no idea how she knew what to do, but Shay just reacted.
She drew both of her hands to her chest, a ball of water forming between them. "Aqua pura..." Raising her hands above her head, the ball of water expands to swirl in an pattern around her hand a wrist. Crossing her arms, Shay threw them forward, the water now rushing in a forceful attack towards the fireball and the monster. "Cleanse!."
The water easily snuffed out the fireball that was heading her way, and continued on toward the pumpkin head thing. She didn't know if it would work, but it stopped the fire.
With the threat no longer heading towards her, she turned to the other girl, hoping she was okay.