Later that year, Katharine was given an audience with the Pope, in which she requested that he send missionaries to help serve in her schools. She was surprised when the Pope suggested that she return and work as a missionary there, herself. After receiving counsel from her spiritual director, she became a novice with the Sisters of Mercy in Pittsburgh, with the understanding that in two years she would begin her own Order. After her novitiate, she founded the Sisters of the Blessed Sacrament for Indians and Colored People. She would dedicate her life and her sizable inheritance, to serving Native Americans and African Americans, to educating them, and to improving their lives. Thirteen sisters joined her in the Mother House of the order at St. Elizabeth's Convent in Bensalem Township, Pennsylvania. Their mission would be to found and staff schools for Native Americans and African Americans throughout the country. By 1942, she had established 40 mission centers and 23 rural schools in 13 states, in addition to Xavier College in New Orleans- founded primarily to train teachers to teach in her schools.
She had inherited $20 million from her father, but she lived under a vow of poverty, and gave all of her inheritance away to the needy and to the work of creating schools and churches. In 1935 she had a heart attack, which forced her to retire to a life of prayer at St. Elizabeth's convent. She remained there until her death at age 96 in 1955. At the time of her death, 501 Sisters in her Order were teaching in 63 schools in 21 states. She was canonized in 2000, two people had been healed from deafness by her intercessions: a man, healed in 1987, and a 17 month old baby healed in 1999. She is the patron saint of racial justice.