The 1980s and 90’s were a rough time for Supergirl and her fans. For starters, she was killed in Crisis on Infinite Earths wiped her from existence. The editorial mandate was with each super-powered cousin, dog, cat etc. Superman loses a bit of his uniqueness. He is no longer the last survivor of a dead world, but one of many and so, the Superman family was shrunk to one.
However, this didn’t stop writers from trying to bring back many of the Super-Family adjusted so that they were not also survivors of Krypton, Superboy was a clone of the Man of Steel, Krypto was a puppy rescued by “Sooperman’s number 1 fan” Bibbo and Supergirl was a shape-shifting alien called the Matrix who dated Lex Luthor Jr. (who was actually the original Lex posing as his own son.)