Or maybe I can make it a bit more complicated, but way cooler. like:

"Each time a spell is absorbed, it lights up a fragment of the shield with an elemental color. when all twelve fragments are lit, Maria can release a blast of the predominant element from the shield, consuming the magic within."

Earth: Lights up yellow. Creates a directional earthquake when released, which can be used to bring down small structures.
Fire: Lights up red. Creates a gout of flame 12 feet long.
Air: Lights up green. Creates a small tornado that disrupts projectiles and light objects caught in it.
Water: Lights up blue. Creates a burst of chill, freezing the area in front of her.