Jennifer was born in Kentucky. Her mother is Catherine Mitchell and her father is Robert Carpenter. She attended St. Raphael the Archangel and then the Sacred Heart Academy. During her last two years of high school, she studied drama at the Walden Theatre in Louisville, Kentucky. She then trained at the Juilliard School in New York City. In 2002, before she graduated, she made her Broadway debut in the revival of Arthur Miller's The Crucible starring Liam Neeson and Laura Linney.Her breakthrough film role was Emily Rose in The Exorcism of Emily Rose (2005). She won a MTV Movie Award for 'Best Frightened Performance' and a Hollywood Life Breakthrough Award. She was also named 'Breakout Performer' at the 2006 Scream Awards.In 2006, she cast as Dexter's adoptive sister in Showtime's "Dexter" (2006). Here she met her first husband Michael C. Hall.