On April 1, 1968, Brunner (age 24) gave birth to Manson's third son, Valentine Michael Manson who he named after a character in Robert Heinlein's book "Stranger in a Strange Land." Brunner, now mother to Manson's child, grew even more loyal to Manson's ideas and to the growing Manson Family.
On July 27, 1969, Brunner was present when Bobby Beausoleil stabbed and killed Gary Hinman. She was later arrested for her involvement in the murder, however received immunity after agreeing to testify for the prosecution.
Her dedication to Manson remained after his incarceration for the Tate-LaBianca murders. On August 21, 1971, not long after Manson was sentenced, Mary along with five other Manson family members, participated in a robbery at a Western Surplus store. The police apprehended them in the act after an exchange of gunfire. The plan for the robbery was to obtain weapons, which could be used to hijack a jet and kill passengers by the hour until authorities released Manson from prison. Bruner was convicted and sent to the California Institute for Women for a little over six years.
It is said that after her release she cut communication with Manson, changed her name, regained custody of her son and is living somewhere in the Midwest.