Williamson attended Houston ISD's Bellaire High School. After graduating, she spent two years studying theater and philosophy at Pomona College in Claremont, California, where she was a roommate of eventual film producer Lynda Obst. In 1973, Williamson—an active antiwar protester—dropped out of college and lived "a nomadic existence" during what she calls "her wasted decade." She moved to New Mexico, where she took classes at the University of New Mexico and lived in a geodesic dome with her boyfriend. She broke up with her boyfriend a year later and moved to Austin, Texas, where she took classes at the University of Texas. After leaving Texas, she went to New York City, intending to pursue a career as a cabaret singer, but got distracted by "bad boys and good dope." "Vanity Fair" wrote that Williamson "spent her twenties in a growing state of existential despair". In New York, Williamson suffered from deep depression following the end of a relationship. She has said that this experience gave rise to a desire to spend the rest of her life helping people.