Who is Mallory Grace from The Field Guide and what is their importance?

Mallory Grace is Jared's older sister. She is thirteen-years-old, and she is described as an aggressive girl who enjoys fencing and is not afraid to fight. It is Mallory, in fact, who starts the fight with the creature in the house by knocking a hole in the kitchen wall and taking out the creature's nest. She is also the first victim of the boggart's pranks. Mallory struggles to get herself to listen to her younger brother, but she is eventually able to control her anger and help him find out about the boggart. Mallory is also able to control her impulse to destroy the field guide and thus continue the adventures of the Grace children with faeries and other mystical creatures.