Life as a nun
As a Carmelite nun, she received the name Louise de la Miséricorde (Louise of Mercy). She sought the most humbling tasks despite her frequent headaches, believing that "nothing was too base for her". She asked to become a lay sister but was only permitted to help novices (who were given the worst chores). She was regularly visited by Rancé (who had been almoner in the Orléans household where she lived as a child), Queen Maria Theresa (who brought along Madame de Montespan twice), and by her childhood friend, Marguerite of Orléans, now Grand Duchess of Tuscany.
One or two years after her entry, Madame Palatine brought La Vallière's son, Vermandois, to visit. When the eight- or nine-year-old wanted to kiss his mother, La Vallière refused him. Even though she would have been allowed to embrace her child because of his young age and despite the entreaties of Madame Palatine and her son’ distress, La Vallière did not relent. Both guests left in tears. She resolved to never see her children again, which the King opposed as he believed that they needed the advice of their mother. The nuns considered it a duty to maintain family ties if it was not for their own pleasure but as a service to others.La Vallière's brother died in October 1676, followed closely by a nun whom she had known from the Orléans household. She envied them but "submit[ed]" to God's will that she would stay alive "as a sacrifice". Her brother had been indebted, and her creditors approached La Vallière. She petitioned the King to allow her nephew to inherit his father's position. In his reply granting the wish, Louis expressed that he would offer his condolences in person if he were a "good enough man to see a Carmelite as holy as" she.
Her daughter, Marie-Anne, continued to be raised by Madame Colbert. In 1680, she married Louis-Armand, Prince of Conti. The prince and his cousin, Henri-Jules, Prince of Condé, visited La Vallière, and he treated his mother-in-law with reverence. She became her spiritual advisor. Her Réflexions was also published for the first time that year. Despite being anonymous, the book alluded heavily to La Vallière's person. Its preface covertly attacked the king and Montespan (who was still his mistress) by saying, "[m]ay Heaven grant that those who followed her in her sins may imitate her in her penance and make good use of the time that the mercy of God gives them to think seriously about their salvation". The book became a success and was soon translated to German.
Aged thirteen, Vermandois joined the libertine circles of Philippe, Chevalier de Lorraine, the lover of Monsieur. After numerous scandals, the king exiled and briefly imprisoned him in Normandy. La Vallière was distressed by her son's fate. On his own request, Vermandois was then deployed to the Spanish Netherlands. Only sixteen, combat took a toll on him; he developed a fever and died on 18 November 1683. In the 18th century, people speculated that Vermandois was the Man in the Iron Mask, declared dead but imprisoned for life. At the time, no one doubted that he had died and he was mourned publicly for his great potential.
The prioress was tasked with informing La Vallière of his death, but she met her before finding the right words. Seeing her sadness and hesitation, La Vallière (who was aware of her son's illness but not of its gravity) said, "I understand well" and went to the chapel to pray. She was never seen to cry for her son, nor did she talk about her grief. A friend advised her that crying could relieve her and that God did not forbid nuns to grieve. "One must sacrifice everything; it is for myself that I must weep", she answered, referring to having children out of wedlock.
In November 1685, her son-in-law died of smallpox, and La Vallière was again "firm and resigned". Lair argues that this was another form of penance: she refused the usual comforts of mourning people to increase the pain caused by her losses. The next year, her mother died; it is unknown how this affected her.
La Vallière continued to look after her family. Her niece by her brother, Louise-Gabrielle, was repudiated by her husband, César-Auguste de Choiseul de Plessis-Praslin, Duke of Choiseul for "misconduct". To protect Madame de Choiseul's sister Marie-Yolande, La Vallière placed her as a pensionnaire in Faremoutiers Abbey and forbade her to contact Madame de Choiseul. In response, Marie-Yolande threatened to kill herself; La Vallière advised the family to let her leave. When Marie-Yolande married in 1697, La Vallière's daughter asked the King for permission to invite Madame de Choiseul. He answered that whatever La Vallière advised should happen, and she allowed Madame de Choiseul to attend. Madame de Conti paid the pensions her mother had requested for relatives and old servants. When the Carmelites wanted to support poor people, La Vallière always turned to her daughter, but she often reprimanded her for her "light" conduct (Madame de Conti's behaviour was often considered inappropriate for widows by contemporaries).
In 1685, working with Bellefonds, she unsuccessfully attempted to convert Gilbert Burnett to Catholicism during his visit to France. Clément claims that she participated in the theological debates of the century concerning Jansenism, which Lair considers doubtful. Foreign dignitiaries frequently visited her, as well as Madame de Montespan after her disgrace in the Affair of the Poisons. She was regularly visited by the Queen, the Dauphine, (Maria Anna of Bavaria), and Marie-Adélaïde of Savoy. In the community, she was appointed sacristine (carer of the oratory). She often fasted on bread and water; after experiencing a memory of the refreshments served at the royal court, she only drank half a glass of water a day for three years. Her physical health was damaged and her superiors urged her to moderate her penance. She suffered from erysipelas but did not seek treatment. She asked to be transferred to "one of the poorest [and] most distant" Carmelite convent, which was refused as the Paris nuns appreciated her company and "example".
Multiple works published during her lifetime discussed La Vallière. A 1678 book by Gatien de Courtilz de Sandras declared that her conversion had reasons other than "spite". In 1695, pamphlets written around 1665 were organised into a book titled La Vie de la duchesse de La Vallière ("The Life of the Duchess of La Vallière"). She became popular among the French; her name was used to sell books to interpret dreams, positioning her as a seer.
At the end of her life, La Vallière suffered from headaches, sciatica, rheumatism, stomach problems, and other unspecified internal ailments. She tried to hide her pain and only complained of having to still live. She was permitted to rise two hours earlier than the others. She did so on 5 June 1710; at three in the morning, she was going to the chapel when pain overcame her. She leaned against a wall, unable to speak, and was found two hours later. Doctors performed bloodletting but concluded that she was dying. She refused to use linen instead of her usual coarse bedding. Seemingly happy about her imminent death, she repeated the phrase, "expiring in the most severe pain, that is what befits a sinner". At night, she asked for Extreme Unction, confessed, and took communion. Abbot Pirot administered the last rites around eleven in the morning. When Madame de Conti arrived, her mother could no longer speak. She died at noon on 6 June 1710. When the King was informed of La Vallière's death, he did not seem moved, saying that she had died for him the day she entered the convent.
According to the convent's customs, La Vallière's body was displayed in the church behind the grille separating the nuns' enclosure. Crowds came to see her and four nuns were necessary to handle the objects people asked to be touched to her body for a blessing. When clergymen arrived to inter the corpse, the laypeople present prayed for La Vallière's intercession with God on their behalf. She was buried in the cemetery of the Carmelite nuns, a small headstone inscribed with her religious name marking the place. The cemetery, including her grave, was desecrated during the French Revolution.
