Regan is caught between her mother's grueling working schedule and the fact that her parents are in the process of an acrimonious divorce (her father is in Europe and is not seen in the film), and she has an older brother named Jamie but he died at the age of 3 because of an infection that wouldn't go away.

She is devoted to her mother, making clay animals as gifts for her and leaving a rose at her place at the kitchen table each morning.

Karras and Father Lankester Merrin (Max Von Sydow) perform an exorcism and succeed in exorcising Pazuzu, albeit at the cost of their own lives.

On the day of the move, Father Dyer (William O'Malley) visits their home and, upon seeing his clerical collar, Regan embraces him, implying she has not totally lost her memory.

For The Exorcist III, Carolco Pictures had the idea of a grown-up Regan who gives birth to possessed twins, but it was abandoned, and the story was switched to Blatty's novel Legion instead.

Regan, with the help of the priests Tomas Ortega and Marcus Keane, finds the strength to once again exorcise the demon from her body and soul, but he retaliates by breaking her back, rendering her paralyzed but still alive.

Actress April Winchell states that she was considered for the role until she developed pyelonephritis, which caused her to be hospitalized and ultimately dropped.