Catherine Cecily O'Brien OP (1893–1945) was an Australian Dominican sister and educationist who was known for her innovative teaching methods and for being an advocate of quality education for girls.

Catherine entered the same Dominican Convent in July 1914, received the habit in April 1915 and took the religious name of Sister Mary Anselm.

[2] Because of her desire to attend university, Sister Mary Anselm moved to Santa Sabina Dominican Convent School in Strathfield in 1921.

Always an advocate for tertiary education, she built up the school's library at Santa Sabina, and organised regular weekly feature lectures on English and Latin literature for the senior pupils and the Sisters.

[6] Sister Mary Anselm O'Brien died in 1945 and the library in the Aquinas Centre at Santa Sabina College is dedicated to her memory.