"In 1876, at the age of 27, she desired to marry an older lawyer who was not to her mother's liking; she argued that her daughter could not marry a "penniless lawyer".[4] Her disapproving mother, angered by her daughter's defiance, locked her in a tiny, dark room in the attic of their home, where she kept her secluded for 25 years. Louise and Marcel continued on with their daily lives, pretending to mourn Blanche's disappearance.
On 23 May 1901, the "Paris Attorney General"[b] received an anonymous letter, the author of which is still unknown, that revealed the incarceration:
"Monsieur Attorney General: I have the honour to inform you of an exceptionally serious occurrence. I speak of a spinster who is locked up in Madame Monnier's house, half-starved and living on a putrid litter for the past twenty-five years โ in a word, in her own filth."
Monnier was rescued by police from appalling conditions, covered in old food and feces, with bugs all around the bed and floor, weighing barely 25 kilograms (55 lb).
One policeman described the state of Monnier and her bed thus:
The unfortunate woman was lying completely naked on a rotten straw mattress. All around her was formed a sort of crust made from excrement, fragments of meat, vegetables, fish and rotten bread... We also saw oyster shells, and bugs running across Mademoiselle Monnier's bed. The air was so unbreathable, the odor given off by the room was so rank, that it was impossible for us to stay any longer to proceed with our investigation."
Her mother was arrested, became ill shortly afterwards and died 15 days later after seeing an angry mob gather in front of her house. Her brother, Marcel Monnier, appeared in court and was initially convicted, but later was acquitted on appeal; he was deemed mentally incapacitated, and, although the judges criticised his choices, they found that a "duty to rescue" did not exist in the penal code at that time with sufficient rule to convict him.[5][7]
After she was released from the room, Monnier continued to have mental health problems. She was diagnosed with various disorders, including anorexia nervosa,[c] schizophrenia, exhibitionism and coprophilia. This soon led to her admission to a psychiatric hospital in Blois, where she died on October 13, 1913, in apparent obscurity." - Wikipedia
Source for that opinion?