Sammie is described as a "petite, pretty, wide-eyed southern belle." She is roughly the same age as her best friend, Kelly Clegg, as they graduated high school in the same year. Sammie married Phil Hagen soon before his military deployment. She discovered she was pregnant soon after. Three years before the start of the novel, the couple had their daughter Emma Lee.
Sammie is a source of companionship for Kelly, who lives alone in Grunwald. She encourages Kelly's idea to interview Gordon Clegg for the local paper. When Emma Lee gets lost in the woods after a car accident, Sammie sustains a minor head injury and is taken to the hospital, preventing her from joining in the search. She is grateful to Kelly for returning her daughter. She convinces Kelly to come to Bellwether and meet with the pastor, Chester Cotton.
When Rachael Flaherty first accuses Kelly of kidnapping her daughter Laylah, Sammie is at first incredulous. But she becomes suspicious when Kelly begins talking about the Axe-Man and the boy in the forest.
She is shown to be reconnecting with Rachael during the kidnapping crisis, and she begins to believe Rachael's claims when Kelly shows up with Ethan. She never shows any malice toward Kelly, however, believing that Kelly is cracking under stress and needs help. She gives information to the police in the interest of preventing Kelly from doing anything with permanent consequences.
Sammie makes one final attempt to reach out to Kelly just before the climax, when Kelly has fled into the woods. Kelly feigns hysteria to feed into Sammie's fear, leading her and the rest of the town to pursue Kelly into the forest. Sammie thus witnesses the Grim Halberdier and Momma Kodi firsthand, realizing Kelly had been telling the truth the whole time. She is quick to apologize and is easily forgiven.
During the final confrontation, she is among the group of mothers who interpose themselves between Kelly and Eld Stagger, an act that restores Momma Kodi's strength. This gives Kelly the realization that leads to Stagger's downfall.