The 34-year-old beat her 81-year-old mother with "objects that were within her reach, a bedside lamp, slats from her bed," the local prosecutor told AFP, adding that she had now been interned in a psychiatric hospital.
The Depeche du Midi newspaper said she had grabbed one of the many crucifixes adorning their apartment in the southwestern town and used it along with other objects to beat her mother to death overnight Monday.
The paper said she had told police: "I had visions in a dream. I saw that I was the devil, that I was evil."
After the murder, the woman called the emergency medical services and was found by them covered in blood and lying at the foot of the bed in which her dead mother lay, officials said.
Lourdes, where Catholics believe the Virgin Mary appeared to a French peasant girl in 1858, received a record nine million pilgrims last year due in large part to Pope Benedict XVI's visit in September.
With thanks to Therese for this story...