As a teenager, De Meester studied to become a teacher and proved to be a competent and kind teacher who was admired and respected by her students. She then decided to leave the school where she taught to be able to serve the poor. On May 4, 1881, she joined the Canonesses Regular of Ypres, Belgium, at the medieval Abbey of Notre Dame de la Nouvelle Plante, to fulfill her calling.
Missionary
In the 1880s the abbey received an appeal from a Catholic priest in the city of Mulagumudu, then in the British Raj, for help in administering an orphanage. De Meester felt that this was an opportunity to serve for which she had longed. With the permission of her superiors she left Belgium, accompanied only by an enthusiastic volunteer novice of the community, and set sail for India. The pair arrived there, only to find that the priest had died during their journey. Though she lacked the understanding and support of the local bishop, Mother Louise and her companion took charge of the orphanage and began to care for the children it housed. To find support in their work, new members of the community were recruited, including local women. To allow for the formation of a sustainable community, De Meester saw that separation from Belgium was needed, otherwise candidates would have to travel to Europe for their religious formation as members of the Order. As a result, in 1897 she established a new religious institute called the Missionary Canonesses of St. Augustine.
Foundress
After establishing missions and schools in India, at the request of the Superior General of the Congregation of the Immaculate Heart of Mary, in 1910 Pope Pius X approved having the Missionary Canonesses work with the Belgian missionary priests in their work in the Philippines. De Meester enthusiastically set out for that nation, accompanied by three companions, Mother Marie Charles, Mother Marie Vincent, and Mother Marie Adeltrude, arriving in Manila on 10 June of that year. From there they traveled to the town of Tagudin, Ilocos Sur, arriving on 21 June, being warmly welcomed by the populace and led to their home in an abandoned friary in the town. They opened St. Augustine's School in the basement of the convent that following 4 July and began to teach, with 225 children enrolled the very first day. That enrollment rose to 300 within a month. De Meester shared the chores of the small community, teaching the children and caring for the house, as well as carrying out her responsibility for the young Congregation. From that small start, the Missionary Canonesses founded what became Saint Theresa's College Manila at San Marcelino in 1915, soon followed by schools and colleges around the nation, including Saint Theresa's College of Quezon City, Saint Theresa's College of Baguio City, and Saint Theresa's College of Cebu City. After the Philippines, foundations were established in China, the United States, the Belgian Congo. De Meester returned to Belgium in 1923 and in 1928 died in Heverlee at the age of 71.
