Joyce Garrard, 46, is accused of forcing Savannah Hardin to run around the family's house near Boaz, Ala., for three hours after she lied about eating a chocolate candy bar, CNN reported Wednesday.
Savannah ran until she collapsed and began having seizures. She later died at Children's Hospital in Birmingham, Ala. A state pathologist ruled the death a homicide.
Garrard is charged with capital murder, which means she could face the death penalty if convicted.
The girl's stepmother, Jessica Mae Hardin, 27, is charged with felony murder, which is a lesser charge. Prosecutors said Hardin was charged for failing to intervene in the punishment.
Attorneys for the two women say Savannah's death was unintentional.