Priscilla Presley is spending time with her granddaughters. On Friday, the 78-year-old former wife of the late Elvis Presley took to Instagram to celebrate Harper and Finley Lockwood's middle school graduation. Harper and Finley, both 14, are the twin daughters of Michael Lockwood and Priscilla's late daughter, Lisa Marie Presley, who died in January at age 54. Riley Keough, who Lisa Marie shared with Danny Keough, was also on hand for the celebration.In Priscilla's pic, she stands arm-in-arm with Riley as they celebrate Harper and Finley's accomplishment.«Happy Graduation girls!» Priscilla captioned her post.