Clark was born as Michael Clark, and served as a United States Navy chief petty officer (E-7), serving as an instructor in anti-submarine warfare. She later underwent a sex change operation and became Joanna Clark; knowing of her past, a U.S. Army Reserves recruiter signed her up for the Army. A year-and-a-half later she was discharged from the Army when her history became known to higher-ups. She brought suit against the Army and won a settlement of $25,000 and an honorable discharge.
During the 1970s, she was an activist for the rights of transsexuals and was instrumental in winning the right of Californians to have their gender changed on their birth-certificates and driver's licenses.
In the 1980s, she felt a religious calling and worked to become an Episcopal nun. Conflict with the church led to her leaving it shortly after she took her vows in 1988, and she has since become a nun of the American Catholic Church, a small independent church using Catholic rites.
In 1990, inspired by meeting an isolated young man with AIDS in rural Missouri, she returned to her family home in San Juan Capistrano, taking on the bulletin board system AEGiS begun by Jamie Jemison and eventually building it into the largest AIDS information database in the world.
She is the recipient of the Award of Courage from the American Foundation for AIDS Research,the Jonathan Mann Health and Human Rights Award from the International Association of Physicians in AIDS Care, the Crystal Heart award from the San Diego GLBT Center and the Joan of Arc award from the Orange County Community Foundation.