An ancient alien theorist from those documentaries on the History Channel, Dr. Ambushius Buggerton theorized that Superman was an alien invader who wanted to take over the world. He was right, obviously. One of his more popular theories was that Supergirl was a gender-swapped Superman. This was proven wrong, but Ambush Bug wouldn't believe it. So, he went on Arkhampedia and wrote the Supergirl article to promote his implausible hypothesis. Nobody cares.