One of four girls, Smithers was raised in the comfortable San Fernando Valley suburb of Woodland Hills just north of Los Angeles, CA. Her father was an attorney. While studying art at Taft High School, Smithers swerved her automobile to avoid hitting another driver and ran into a telephone pole. The accident left a permanent scar on her chin. A couple of years later, Smithers was interviewed by Newsweek reporter David Moberg for a story about typical American teenagers in the 1960s. She was photographed happily riding the back of a friend's motorcycle by Julian Wasser. That carefree looking shot made the cover of the March 21, 1966 issue of the magazine. The shot led to work in commercials while she was continuing her art studies at California Institute of the Arts in Valencia.

After a few years as a working actress, she won the role of pretty but shy Bailey Quarters in WKRP in Cincinnati, a CBS sitcom about a midwestern radio station. After the show ended its run, she worked on occasion and in 1987, married actor James Brolin. She became a stepmother to his two sons and had a daughter with Brolin. Her marriage to Brolin ended in 1995.
Featured on the cover of a 1966 Newsweek in a feature story on American teenagers Dismissed stories that singer Barbra Streisand had ruined her marriage to James Brolin, by pointing out that she and Brolin had parted (amicably, sharing custody of their daughter) a full five years before Streisand and Brolin got together. She mentioned in an interview show in 1985 that she had been married briefly at the age of 20, but that it didn't work out. The name of the spouse was never mentioned.