Cher loves her mom. No reason to think Rihanna doesn't, but for now, the career comes first. Two of pop's highest-profile divas take the spotlight in new docu-specials, with Lifetime's Dear Mom, Love Cher (Monday, 10/9c) going for the heart-strings as Cher pays tribute to her 86-year-old mom, Georgia Holt, who uprooted her family from Arkansas to Hollywood to pursue stardom that would take another generation to achieve. Cher performs a duet with Georgia and introduces recordings her mom taped more than 30 years ago that Cher is preparing to release commercially. Think of this as a helpful reminder if you haven't done your own Mother's Day shopping yet. Rihanna's love-fest in Fox's self-promotional vanity production Rihanna 777 (8/7c) is with the fans who follow her on a world concert tour, packing a 777 airliner along with journalists and a film crew capturing her every move.