"Estelle is gone," Spector said in a posting on her Web site dated Wednesday. "To my beloved sister, rest in peace. You deserve it."
No details regarding the cause or location of Bennett's death were given.
Bennett, Spector and their cousin Nedra Talley were from the Washington Heights section of Manhattan and went on to perform as the Ronettes, recording hits like "Be My Baby" and "Walkin' in the Rain" before breaking up in 1966. Bennett recorded one solo record -- "The Year 2000/The Naked Boy" -- before she retired to raise a family, the New York Daily News noted.
The Ronettes reunited only once, for their 2007 induction into the Rock and Roll Hall of Fame.