By his second wife, Barbara’s mother, Peter Koob had five children in Germany and five children in the United States. In 1839, the year following Barbara’s birth, the family immigrated to the United States to seek opportunity.
The Koob family settled in Utica, New York and became members of St. Joseph Parish, where the children attended the parish school. In 1848, Barbara received her First Holy Communion and was confirmed at St. John Parish in Utica when, in accordance with the practice of the time, the bishop of the diocese came to the largest church in the area to administer these two sacraments at the same ceremony.
Barbara, in August, 1862, entered the Sisters of the Third Order of Saint Francis in Syracuse, N.Y., and, on Nov. 19, 1862, she was invested at the Church of the Assumption. She soon became known as Sister Marianne.
Mother Marianne, in 1877, was elected Second Provencial Mother of the Syracuse Franciscans. In 1883, she received a letter from a priest in Hawaii begging for help on behalf of King Kalakaua and Queen Kapiolani for the Kingdom of Hawaii. From 50 other religious communities in the United States, only Mother Marianne's Order of Sisters agreed to come to Hawaii to care for people with Hansen's Disease (known then as leprosy).
The Sisters arrived in Hawaii on November 8, 1883, dedicating themselves to the care of the 200 lepers in Kakaako Branch Hospital on Oahu. This hospital was built to accommodate 100 people, but housed more than 200 people. The condition at the hospital were deplorable. Each Sister-nurse learned to wash the fetid wounds, to apply soothing ointment to the wounds, and to bring a sense of order to the lawlessness that prevails when there is abandonment of hope.
Mother Marianne founded Malulani Hospital, Maui's first general hospital for the ordinary sick on that island a year later. In 1885, realizing that healthy children of leprous patients were at high risk of contracting the disease, yet had no place to live, she founded Kapiolani Home on Oahu for healthy female children of leprosy patients. Because of her work, she was the recipient of the Royal Medal of Kapiolani.
In the summer of 1886, the Sisters took care of Father Damien when he visited Honolulu during his bout with leprosy. He asked the Sisters to take over for him when he died.
Mother Marianne led the first contingent of Sister-nurses to Kalaupapa, Molokai, where more than a thousand people with leprosy had been exiled. Upon arrival, on November 14, 1888, she opened the C.R. Bishop Home for homeless women and girls with Hansen's Disease. To improve the bleak conditions, Mother Marianne grew fruits, vegetables, and landscaped the area with trees thus creating a better environment among the residents.
While at Kalaupapa, Mother Marianne predicted that no Franciscan Sister would ever contract leprosy. Additionally she required her sisters use stringent hand washing and other sanitary procedures.
Upon the death of Blessed Damien on April 15, 1889, Mother Marianne agreed to head the Boys Home at Kalawao. The Board of Health had quickly chosen her as Father Damien's successor and she was thus enabled to keep her promise to him to look after his boys. The Boys Home at Kalawao was completely renovated between 1889 - 1895 during her administration. During the renovation, it was renamed Baldwin Home by the Board of Health in honor of its leading benefactor, H.P. Baldwin.
The two new Sisters who came to run the Home were accompanied on their boat journey by poet Robert Louis Stevenson, who stayed for a week. During his stay, he wrote a poem for Mother Marianne and later donated a piano so that "there will always be music."
Mother Marianne's spirit of self-sacrifice enabled her to live and work with leper patients for 35 years. Although there was not yet a cure, the Sisters could offer the lepers some semblance of dignity and as pleasant a life as possible.
Mother Marianne died in Kalaupapa on August 9, 1918. The Sisters of St. Francis continue their work in Kalaupapa with victims of Hansen's Disease. No sister has ever contracted the disease.