In 1915 she decided to dedicate herself to the missionary field. She was accepted as a missionary in the General Assembly in London in June 1915. She took a training course at St. Colm's College, Edinburgh, and on 23 Oct. 1916 sailed from Liverpool and arrived in Calcutta on 28 Nov. For ten years she served in the Sylhet district on the lowlands of Khasia and Jaintia, where the Hindu caste system was in force and respect towards women was low. By April 1918 she had been promoted headmistress of the Williams Memorial School for girls and had become fluent in Bengali . She showed unusual ability as a teacher and possessed organising skills. She decided to identify herself with the natives by adopting their dress, their customs and food. She frequented their Zenanas regularly. She preached in Bengali and taught the girls to knit and sew . The Sunday school flourished under her charge. In 1923 she went to Maulvi Bazaar and stayed there for two years. She was invited to become headmistress of the language school in Darjeeling which was under the patronage of the Bengal and Assam Christian Council. Gandhi when he visited the school was amazed at her mastery of the language. On the strength of her linguistic brilliance she was seconded to study for the M.A. degree in Indian Vernaculars at the University of Calcutta. She was awarded the degree (first class) by examination in 1926 with a University prize (£200 worth of books) and a gold medal for her excellence in every subject . She was the most brilliant of the students. She stayed at the language school from 1925 to 1931 .
She returned to Wales on furlough in 1930 and registered at the Sorbonne in Paris to study for a doctorate. (She had already spent 1928-29 at the University of Calcutta ). By virtue of the excellence of her M.A. degree and on the special recommendation of Professor S.K. Chatterji, Calcutta, she was allowed to present her thesis within the year. He said of her, in a letter dated 15 April 1929, ‘ With her first-rate knowledge of Bengali and her intimate knowledge of the original texts, and her close association with Bengali life and culture, she is equipped for the work in a way which few foreigners can expect to be … ’. She was awarded the degree of Docteur de l'Université de Paris for a thesis on the subject ‘La femme bengalie dans la littérature du moyen age’. There is a copy of this work in the library of the University of Wales, Bangor. She was offered chairs in Bengali by universities in Britain, America and India but declined them and returned to teach, direct and evangelise at Karimganj, Assam. She accepted an honorary professorship of English and Bengali at the Indian Government college in Karimganj . However, her name is mainly associated with Dipti Nibash (Home of Light), as it was there that she established a home for widows and orphans in need of care . There they made jam, cloth, handkerchiefs, stockings and grew rice as well as cultivating the land and producing silk. The women were trained to use the spinning-wheel and taught to be self-sufficient.
She was very supportive of the ecumenical movement which strove to establish a Presbyterian church for the whole of India. As a Swarajist she believed in church freedom and self-government, and succeeded in getting the women's work organised separately within the Assembly. She planned the Pracharikas (a women's evangelical order) and acted as the Assembly's clerk for twenty years. She was elected Moderator of the Assembly of the Lowlands. She was a regular contributor to the press especially Y Cenhadwr, Y Goleuad, The Treasury, not to mention her reports to the Foreign Mission. She published an English journal jointly with the Rev. Lewis Mendus, The Link. She translated Reality and religion, Search after reality and Sermons and sayings by Sadhu Sunbar Singh into Bengali, and wrote a biography of the author. She composed two missionary plays, Chumdra Hela and Dydd y pethau bychain. She was friendly with Rabindranath Tagore and R. Kanta Sen and translated some of their poems into Welsh and English (see Y Cenhadwr, Feb. 1930 ). She d. suddenly in Karimganj on 12 Feb. 1955, and her grave is there in front of the chapel. The library of Karimganj college is named ‘Rowlands Hall’ in her memory and there is a memorial to her in the chapel (CM) in Menai Bridge.