A Promise to Carolyn (1996)

Flashbacks in the early part of this fact-based film set in McKinney, Texas, establishes that three sisters were mistreated by an abusive step-mother. 37 years later, the two remaining sisters still are haunted by the treatment they received and begin to be haunted by the supposed accidental death of the third at the step-mother's hands. With the help of a detective, a District Attorney, and through hypnosis, the two sisters piece together the step-mother's crime and have charges brought against her.