Anderson was the name listed on the ultrasound for Maggie Duvall--then Maggie Anderson--and Brandon James's child before they were put up for adoption. This child was one of Emma and Maggie's prime suspects. Emma theorized that the child may have returned to get revenge for being given up.
After a teenage Maggie caught her future husband, Kevin Duvall, cheating on her with one of her friends, Maggie and Brandon James had sex, which resulted in Maggie being pregnant with Brandon James's baby. Her parents arranged for her to leave town during the pregnancy and give up the baby in a closed adoption, since she was only sixteen and could not support a baby. She didn't even know if the baby was a boy or a girl.
Scream (TV Series)
The ultrasound was first seen on the wall of the killer's lair in Aftermath.
Maggie confessed to Emma about having the baby with Brandon James in Ghosts.
In Revelations, it was revealed that the ultrasound was of a prenatal Piper Shaw. She was the child of Brandon James and Maggie DuvalL, making her Emma's half-sister.