Catherine de Bar was born on 31 December 1614 in Saint-Dié in Lorraine. When she was barely 17 she entered the Monastery of the Sisters of the Annunciation in Bruyères. In the confusion of the Thirty-Years War the community fled from the advancing Swedes. In 1638, together with some of her sisters, Catherine found refuge with the Benedictine nuns in Rambervillers. She discovered her true calling in the Benedictine way of life and decided to transfer to this order. In 1639, Catherine was vested with habit, receiving the name Mechtilde. A year later she made her profession. In 1641, forced to flee once again by the war, Sister Mechtilde arrived in the Benedictine monastery at Montmartre in Paris. There she appreciated the spiritual training of the abbess and the monastery, but she left the abbey again after a year, in order to gather together the sisters of Rambervillers who had become scattered. During the next few years she stayed in various places, finally returning to Paris. Supported by Duchess Marie de Châteauvieux, Mother Mechtilde, who had meanwhile become the prioress of the community at Rambervillers, was able to acquire a house in the Rue Férou in the Saint-Germain quarter of Paris, which she moved into with her sisters and turned into a monastery. For some years Mother Mechtilde had had the wish to devote herself in a special way to the adoration of Christ in the Sacrament of the Eucharist. However she was hesitant about introducing this form of worship into her community. Queen Anne of Austria came to hear about the little monastery of Benedictine nuns through a priest. She had taken a vow and wanted to help found a convent of perpetual adoration. Her choice fell on the house in the Rue Férou.
