Guérin was born on October 2, 1798, in Étables-sur-Mer, France. Her father, Laurent Guérin, was a naval officer in the service of Napoleon and was killed by brigands near Avignon while returning on furlough just before the Russian campaign. Her mother, Isabelle LeFèvre, was a member of a family of the lesser nobility.
Guérin attended a private school in Étables and later continued her education under a tutor.
In 1823 Guérin entered the community of the Sisters of Providence at Ruillé-sur-Loir, founded by Abbé Jacques Dujarié in 1806. As Sister Theodore, she showed unmistakable signs of her aptitude for the religious life and the work of education. Immediately upon taking her vows she was appointed superior of the establishment at Rennes. After ten years at Rennes, she was transferred to Soulaines, where she received medallion decorations for the excellence of her teaching. There also she pursued a four years' course in medicine and pharmacy under the noted Lecacheur, a course which proved invaluable in her later labors. In answer to an appeal made to the community at Ruillé-sur-Loir, by Rt. Rev. Célestine de la Hailandière, Bishop of Vincennes, Indiana, for sisters for his diocese, six sisters with Mother Theodore as superior set out for America on July 26, 1840. After many hardships, delays, and disappointments, the little company arrived at Saint Mary-of-the-Woods on October 22. Here in the wilderness she established the first academy for young women in the state, chartered in 1846 with powers to confer academic honors and degrees. Upon her death in 1856, she left behind her an institution securely founded, a growing community, a flourishing academy, and a number of thriving schools in various towns of Indiana. Mother Theodore was not only an educator, but an organizer of extraordinary ability. Her extensive correspondence with ecclesiastics, national and local authorities, her carefully kept diaries, annals, and journals of travel, are rich sources of information for the biographer and the historian. And in addition to her rare intellectual qualities, she possessed a deep spiritual nature, a masterful power of training religious educators, and the soul of a missionary.
