Maiden name taken from wikipedia entry for husband Victor John Mature. Per Find A Grave contributor Nancy Shelton (49381992), Loretta Mature is still alive as of July 2019. There is also an inscription on the opposite site of the stone with the name of their daughter, opera singer Victoria Mature, who at the time of this research was still living.
From Find A Grave contributor anony1234 (47047632):
"Lorette" was the daughter of Charles Conrad Sebena and Laura Beth Fontanella, per the "Illinois, Cook County, Birth Certificates" database.