The Mademoiselle was an emissary of the Shrouders, possibly an artificial intelligence, who was imprinted on the brain of Carine Lefevre when the latter entered Lascaille's Shroud. She returned to Chasm City in Lefevre's body and secretly became a major underworld figure, with the ultimate goal of making sure Sun Stealer was prevented from provoking the Inhibitors.
She transferred a beta-level simulation of herself to a disguised implant in Ana Khouri's head to ensure her mission to the Delta Pavonis system was completed. The Mademoiselle's motivations were unclear at the time, and her ruthlessness was apparent when she attempted to destroy the planet Resurgam to keep the inhabitants from inadvertently alerting the Inhibitors. That beta simulation was lost during the struggle against Sun Stealer for control of Nostalgia for Infinity. Sun Stealer subsequently succeeded in alerting the Inhibitors, although it was later destroyed by the humans on board the Nostalgia for Infinity.
Her original body was apparently killed by H, who took over her enterprises, but some remnant of her lived on inside Skade's brain -- disguising itself as the voice of the "Night Council". This manifestation, aware of the failure of the original Mademoiselle to destroy Sun Stealer, instead focused on attempting to ensure that the Conjoiners re-acquired the Cache Weapons in order to combat the Inhibitors. She failed in this endeavor as well, and was presumably killed with Skade.