Amongst her first commissions was the St Ita window for St Brendan's cathedral in Loughrea in 1904, which was designed by Sarah Purser. O'Brien joined An Túr Gloine in 1906, beginning her career there by designing Angel of the Annunciation window in the Enniskillen convent chapel. For a window in the Wilson private chapel Coolcarrigan, Naas, County Kildare in 1912, O'Brien incorporated Celtic design, some drawing on the Book of Durrow. In 1914, she toured the cathedrals of Paris, Rouen, and Chartres with Purser and Wilhelmina Geddes. O'Brien designed three windows depicting St John, St Flannan, and St Munchin, for the Honan Chapel in University College Cork in 1916. Her 1923 design of the centenary memorial window in St Andrew's church, Lucan, represented the parable of the Good Shepherd. When in 1925 An Túr Gloine became a cooperative society, O'Brien became a shareholder along with Ethel Rhind, Evie Hone, and Michael Healy. Her 1926 lunette The spirit of night represented night, twilight, and dawn, and was for the private home of Keng Chee Roselands in Singapore, the building was later demolished. The window of St Catherine of Siena for the Sacred Heart convent chapel, Newton, Massachusetts dates from 1927. O'Brien's 1931 St Patrick window, for the De La Salle school, East Coast Rd, Singapore, commissioned by architect Denis Santry, and is the only extant stained-glass work by an Irish artist in that country. Much like Rhind, O'Brien also employed opus sectile, such as in her 1936 Mass in penal days in the Franciscan friary, Athlone, County Westmeath. O'Brien contributed two windows, Pelican and lamb and Host and chalice: wheat and grapes, to the ten windows An Túr Gloine produced for Brophy College Chapel, Phoenix, Arizona in 1937. From 1937 until 1947, O'Brien worked on 22 opus sectile panels for the Protestant Church in Ennis. Purser retired from An Túr Gloine in 1940, and O'Brien succeeded her as director, going on to purchase it and the contents in 1944. O'Brien rented a section of the premises to fellow stained-glass artist Patrick Pollen from 1954 onwards. O'Brien exhibited at the 1953 Irish Exhibition of Living Art, and the 1958 exhibition of the Arts and Crafts Society of Ireland. When the An Túr Gloine studios were fire damaged in 1958, she rebuilt then and reopened by 1959. O'Brien was an active member of the Soroptimists and the Guild of Irish Art Workers. The last work she completed was a three-light window for St Multose's church, Kinsale in 1962. A commission for two windows for the private chapel of Áras an Uachtaráin for President Éamon de Valera was left unfinished at her death.
Death and legacy
O'Brien died in Sir Patrick Dun's hospital, Dublin on 18 July 1963. She was buried in Whitechurch graveyard, County Dublin. She is commemorated in a window designed by Pollen in St Laurence O'Toole chapel, Christ Church Cathedral, Dublin, where for forty years she made floral arrangements. Over 150 of her An Túr Gloine drawings from notebooks are now in the National Gallery of Ireland.
