Born in Chatham, Ontario, Canada, Susanna Carson was dedicated to missions at age 11, when her father, a Methodist school inspector, registered her for medical school. She graduated from Toronto Women's Medical College in 1888, in its second class. In 1894 she married Petrus Rijnhart, who had joined the China Inland Mission (CIM) in 1890. Stationed in Lanchow (Lanzhou), Kansu (Gansu) Province, the last Chinese city on the Silk Road before central Asia, Susanna and her husband were influenced by Annie Royale Taylor, the "lone wolf of Tibet," and Cecil Polhill-Turner of the Cambridge Seven. In 1893 the CIM summarily dismissed Petrus Rijnhart, claiming that he was an imposter.
Supported by the Disciples of Christ in Toronto, the Rijnharts traveled six months to Tsinghai (Qinghai) Province, or Outer Tibet. At a Buddhist monastery they became friends with a Living Buddha and witnessed a battle between Tibetans and Muslims. After four years on the border of Tibet, they set out with their infant son and enough food for a year to walk to Lhasa, the Tibetan capital. During the nightmarish journey the baby died and Petrus, seeking help from some nomads, disappeared. Two months later Susanna stumbled into Tatsienlu (Kangding), Szechwan (Sichuan). Recuperating in Toronto, she wrote With the Tibetans in Tent and Temple, a testament to her husband's "burning ambition to be of service in evangelizing Tibet-whether by his life or his death, he said, did not matter." In 1902 she returned to Tatsienlu with a few Disciples of Christ missionaries, where she married James Moyes of the CIM. When her health failed, they returned to Chatham in 1907. She died there a year later, perhaps of complications from childbirth.