The parents of Mademoiselle De La Mothe had both sustained the marriage relation previously to their marriage with each other. And each of them had a daughter in their first marriage. These two daughters, acting on the principles and methods of personal consecration which are recognized in the Roman Catholic church, had devoted themselves to a religious life in the Ursuline Convent, and thus became associated in its system of instruction. After having been taken from the Benedictine Seminary, and spending some time at home in a manner not very profitable, Mademoiselle Jeanne Marie, their young half-sister, who had already spent a little time there in her early childhood, was once more placed at the Ursulines with them. She was now in the seventh year of her age. The father, who seems to have been sensible, from what had fallen under his own notice, that her education had hitherto failed to receive sufficient attention, commended her to the especial care of his own daughter, as the best qualified of the two half-sisters, by kindness of disposition as well as in other respects, to aid in the development of her mind and the formation of her manners. In her after life, as she recalled with gratitude the dealings of God with her in her younger years, she spoke in affectionate terms of this sister, as a person characterized alike by good judgment and by religious sentiments, and as especially fitted to train up young girls.
This good sister employed her time in instructing me in piety, and in such branches of learning as were suitable to my age and capacity. She was possessed of good talents, which she improved well. She spent much time in prayer, and her faith seemed strong and pure. She denied herself of every other satisfaction, in order that she might be with me and give me instruction. So great was her affection for me, that she experienced, as she told me herself, more pleasure with me than anywhere else. Certain it is, that she thought herself well paid for her efforts in my behalf, whenever I made suitable answers on the studies in which I was engaged. Under her care I soon became mistress of most of those things which were suitable for me; so much so that many grown persons, of some rank and figure in the world, could not have exhibited such evidence of proficiency and knowledge as I did.
— edited from The Life of Madame Guyon Volume 1, Chapter 2.