Jilly Cooper, the bestselling British author known for her chronicles of class and sex in risqué novels, including “Rivals” and “Riders,” has died unexpectedly, her agent and family said Monday. She was 88. The author died on Sunday after a fall, according to a statement from literary agency Curtis Brown, who represented her. “Mom was the shining light in all of our lives,” her children, Felix and Emily, wrote. “Her unexpected death has come as a complete shock.” Cooper garnered scores of fans