Mother Theresa was educated by the Oblates from her sixth year. Born Sarah Willigman, she was baptized at St. John's Church (now St. Alphonsus) in Baltimore, Maryland. When her mother died, Sarah and her sister, Charity, were brought to the Oblates and left in their care.

Although she was Father Anwander's first applicant, she was deprived of her hoped for name "Alphonsa." Sarah's reception into the community was delayed by a suit against the Sisters by her non-Catholic family. Charges were brought that she was being coerced to enter religious life. A decision was rendered in favor of the Sisters. By the time the case was settled, another Sister had received the name Alphonsa.

Mother Theresa was a woman of great piety and humility. She wrote the history of the community from the time Father Joubert's diary stopped, telling details of everyone but herself. For many years, she was secretary and assistant to Mother Louise Noel. As principal of Saint Frances Academy, Mother Theresa Catherine preserved the culture and refinement developed in her by the Sisters. She taught French, English and music and also gave instructions in domestic science, tapestry and sewing. For 24 years she was vicar, first under Mother Gertrude and then under Mother Louise. Humility, kindness, devotion to duty, love for the community were characteristic of her through the years. It was no surprise, then, that she was elected Superior when Mother Louise died.

Mother Willigman's administration was burdened with money worries. A natural fund-raiser, she reduced the Motherhouse debt from $13,000 to $900 and lived to see the chapel of her dreams a reality. Always she held fast to the vision of Mother Mary.

In 1888, Mother Theresa sent four Oblate Sisters to Leavenworth, Kansas. A new ministry in the Oblates' history, the care of destitute boys, was begun. Mother Theresa never forgot what it felt like to be an orphan; she could never refuse any plea made in behalf of orphans.

In 1892, she sent Sisters to Washington, D.C., where they bagan service at St. Cyprian's School. This was the first parochial school staffing attempted by the Oblate community. In 1896, the last year of Mother Theresa's administration, the Sisters began the practice of wearing silver rings as a sign of faithfulness in the religious life.

Mother Theresa's hearing failed her, making the service of guiding the community very difficult. In 1897, she was succeeded in office by Mother Mary Magdalen Cratin. Mother Theresa lived until 1912, long enough to celebrate in 1901, the Golden Jubliee of her religious profession.