The summer of her junior year, Spang auditioned to be an apprentice at Williamstown Summer Theater. A year later, Scott set up an audition for Spang at the American Academy of Dramatic Arts. She received a scholarship and graduated from there two years later. Following graduation in 1969, Spang returned to Michigan where she attended Adrian College, living dorm life on a small campus, but not far from her family in Ann Arbor.

After a Universal Studios talent agent spotted her in 1972, Spang signed a 7-year contract with the studio. She then had a succession of guest-starring roles in television series including Emergency!, Adam-12 (Episode: Venice Division), The Streets of San Francisco, The Six Million Dollar Man, Happy Days, Chase, The Secrets of Isis, Charlie's Angels and Lou Grant. Spang also appeared in the television movies Short Walk to Daylight, Runaway! and Sarah T. - Portrait of a Teenage Alcoholic. She co-starred in a production of Winesburg, Ohio on KCET's Hollywood Television Theatre.

Spang married actor John McCook on February 16, 1980; the couple have three children.

Spang's later acting performances were in The Love Boat, Fantasy Island, The Dukes of Hazzard and Magnum, P.I.. She took a de facto retirement from acting in 1984, though she made a brief appearance in the 2007 horror film Plot 7, which also featured her by-then husband John McCook. In 2002, Spang appeared in the Battlestar Galactica episode of Sciography documentary series on the Sci-Fi Channel in 2002. In 2003, she appeared in another Battlestar Galactica documentary included as an extra feature in the DVD box set of the series released for the series' 25th anniversary.