Alice Mildred Cable was born in Guildford, England. She decided at age 15 to become a Christian missionary, and over the objections of her parents, went to London to train as a pharmacist. In 1901, she joined the China Inland Mission and took ship for China, despite the outbreak of the Boxer Rebellion, leaving behind a fiancé who was reluctant to take the risk. In China, she met Evangeline (Eva) French, who became her senior missionary. Together they opened a girls’ school in Huozhou and proselytized in the surrounding villages.
In 1908, Mildred and Eva returned to Britain on furlough, and met up with Eva’s younger sister, Francesca French, who decided to join them in China. The three women became known as "The Trio" and worked together for the rest of their lives. In 1923, they set out on an itinerant ministry, traveling 1,000 miles along the Silk Road from Gansu province to Xinjiang province, a journey that took nine months. The following year, they moved up the Silk Road and settled in Jiuquan, the last town in China before the start of the Gobi Desert. They later followed the Silk Road northwest across the Gobi Desert and on to the Russian border. After another furlough in the UK, they returned to travel and work in Tibet and Mongolia. After 1936, they were unable to return to Asia and retired to Dorset, England, where they wrote numerous books and articles about their experiences. In 1943, they published The Gobi Desert: The Adventures of Three Women Travelling Across the Gobi Desert in the 1920s, which is still recommended in guidebooks today.