Disclaimer: I own none of the characters from Elseworld's Finest, they all belong to DC comics. The comic book itself sprung from the mind of Barbara Kesel and the artists Matt Haley and Tom Simmons, all of whom deserve much thanks.
Elseworld's Finest Females: Supergirl and Batgirl
History, despite what many might think, is remarkably mutable. The river of time can be changed by a mere pebble, and the world that we are familiar with can be overturned and remade into something entirely different. So it is in this case...
It was chance that brought two families to the movie theater to watch the Mark of Zorro. Outside, Joe Chill attempted to rob the Wayne family but Jim Gordon intervened, a cop to his core. He paid for that with his life as Joe killed him and his wife, but Barbara Gordon picked up his gun, a child no more, and stopped the killer.
Orphaned Barbara was taken in by the Wayne family, and secretly began preparing. First she found the cave beneath the manor, developed the electronic systems of Oracle, published her first novel on crime to pay for her crusade then finally was discovered by Bruce, her big brother who put the final touches on Batgirl.
Similar chance sent a rocket hurtling from Krypton even as Argo city was blasted free, the domed construct surviving for a time in the depths of space. As Kryptonite radiation slowly seeped through the protective shields Zor-El took his healthy daughter Kara and transported her to Earth in a rocket, feeding her with data on her new world.
Enchanted by Earth's superheroes she was found by Wonder Woman and her Justice Society, and the young lady eagerly asked to join. A Justice Society with Abin Sur and Shiera Thal, both aliens who had visited Krypton and were willing to share their memories with the homesick girl. A Homesick girl whom was eventually befriended by business tycoon and Society supporter Lex Luthor, who became almost a surrogate big brother to her.
Before Supergirl joined the Justice Society Batgirl had forcibly banned superhumans from Gotham, reasoning that with no superhumans there would be no super criminals, the Oracle system helping enforce that threat. The Justice Society went to war against Batgirl, including Black Canary, Captain Marvel, Revenant and others, and were stunned when they were defeated by the well prepared and ruthless hero.
Yet they were even more surprised, if possible, to be invited back into Gotham along with Lex Luthor to unveil a Wayne Corp and Lexcorp collaborative venture. Barbara Gordon and Bruce Wayne hosted the event, but afterwards Luthor was kidnapped by a old business associate. In the course of the investigation Supergirl and Batgirl were forced to work together and even developed some mutual respect, even as Batgirl helped Supergirl deal with some stunning revelations.
Supergirl was NOT the first child of Krypton to land on Earth. Lex Luthor and Emil Hamilton were there when baby Kal-El's rocket crashed, and they ruthlessly killed the child. Using technology derived from the child's solar powered cells and his ship Luthor made billions, uncaring that he had snuffed a child's life. Much like, as Batgirl now knew, he had ordered the deaths of the Waynes and had instead killed the Gordons.
Batgirl televising his gloating speech across the city via Oracle helped bring him down, but Supergirl was shaken to the core to discover a man she thought of as a friend was instead a monster and a murderer. In the aftermath Supergirl spirited the child's remains away for a proper burial even as Batgirl took Luthor's Kryptonite ring and hid it in a valut, just in case she might need it in the future.
To be continued...
Notes: this is a rough summary of Elseworld's Finest Supergirl & Batgirl, published back in 1998. Barbara Kesel does a MUCH better job of telling the story there, and I urge you to read it!