In 1955, she moved to California, and became involved with the art scene surrounding the Ferus Gallery. That year she created the experimental "Instant Theatre," within the Cast Theatre (now named El Centro Theatre), performing in and directing it for ten years. She was a leading figure in the L.A. Women's Art Movement in the 1970s and co-founded the Womanspace Gallery, a cooperatively run gallery devoted to work by female artists, in 1973. She is considered one of the "first-generation feminist artists," a group that also includes Mary Beth Edelson, Carolee Schneeman, and Judy Chicago. They were part of the Feminist art movement in Europe and the United States in the early 1970s to develop feminist writing and art. By 1975, she had written, created, directed and acted in more than 30 full-length performances in the United States and Europe. Rosenthal began teaching classes in performance in 1979.