Mary Cain was better known as Sister Mary de Ricci. She served the Maryknoll Sisters and was sent to Hong Kong in 1927. Prior to the Pacific war, Sister Mary de Ricci worked at Maryknoll Convent School in Kowloon and Holy Spirit School on Caine Road. She later became House Superior of Holy Spirit School.
In December 1941, she resided in the convent in Holy Spirit School. After the fall of Hong Kong, the Sisters at the convent worked at Queen Mary Hospital to help care for the wounded. On 21 January 1942, Sister Mary de Ricci and her group of Sisters from Hong Kong Island were interned at Stanley Camp.
In September 1942, Sister Mary de Ricci and other Maryknoll missionaries were released from confinement (see here). After gaining permission from the Japanese authorities, she left Hong Kong and worked in the inland missions of China. In 1945, Sister Mary de Ricci together with Sisters Mary Dorothy and Mary Eucharista made their way to India. In 1946, they returned to Hong Kong.
Sister Mary de Ricci remained in Hong Kong and continued her life's work in the field of education. She is buried in St. Michael's Cemetery in Happy Valley.
Source
1. Maryknoll Mission Archives: https://maryknollmissionarchives.org/deceased-sisters/sister-mary-dericci-cain-mm/
2. Sister Mary de Ricci: https://archives.catholic.org.hk/In%20Memoriam/Religiou%20Sister/MR-Cain.htm
3, The Maryknoll Sisters in Hong Kong. See here
4. The St. Louis Review dated 30 October 1942. See here