Brunner was born in Eau Claire, Wisconsin to George and Elsie Brunner. She moved to California upon graduating from the University of Wisconsin–Madison in 1965 and took a job as library assistant at University of California, Berkeley. She met 33-year-old career criminal Charles Manson who had been released from Terminal Island prison several weeks earlier. She let him stay at her apartment and the two became lovers after several weeks. She was thus the first person whom Manson recruited into his "Family". She quit her job and the two began to drift around California in a van meeting other young women.