Modeste was born in 1884 and was the second before last daughter of Régis Lavoie and Sophie Thériault from Saint-Basile. By means of a scholarship given to her by her uncle Placide Thériault, Modeste was a student boarder at the convent for seven years. Placide Thériault and his wife Marie-Anne Levasseur had made a donation to the Sisters of Saint-Basile Convent and lived there. Placide died in 1898 at the age of seventy-nine. The Chronicles reveal that their donation was very beneficial to the convent. Modeste went to Normal School in Fredericton, in 1902. After having taught for six years, she joined her sister Claudia who was already a sister at Hôtel-Dieu in Saint-Basile.