Maggie is a supportive presence throughout the book, providing Kelly with encouragement, companionship, and food during the adventure. She believes Kelly about seeing Momma Kodi in the woods, and she lets Kelly into the library archives to help her learn more information about the Grim Halberdier.
It is Maggie who comes up with the plan for Garrett to fake a reason to abandon Kelly, letting Chester Cotton think he is in the clear to make his move.
At the climax, Maggie first tries to run Eld Stagger down with Kelly's car. She then takes a stand with Kelly's Mother, Sammie Hagen, and Rachael Flaherty to protect Kelly from being killed by Stagger. This action restores Momma Kodi's strength, allowing Kelly to make the realization that leads to Stagger's defeat.
Maggie is last seen serving as a volunteer at Vacation Bible School, welcoming her newly adopted grandson, Ethan Levi Clegg.