In a Pocket Universe alternate reality, three Kryptonian criminals escaped the Phantom Zone and tried to take over that reality's Earth. There was no Superman in this reality (his younger self, Superboy, having died before the criminals' escape) but there was a Lex Luthor who hadn't gone bad. Using an artificial life form called the 'protoplasmic matrix', Lex made a red-headed woman who resembled his true love, the deceased alternate reality Lana Lang, even having Lana's memories due to her synaptic pathways being copied into the creature. This Lex had also patterned her physiology to resemble Superman's, whom he had seen using one of his many inventions to look into another universe.
Like Superman, the creature was super humanly strong and fast and could fly, but also had the powers of shape shifting, telekinesis, and invisibility. The girl, whom Luthor called Matrix, was given a feminine version of Superman's uniform, shape-shifted into a young blonde woman, and fought the three criminals as "Supergirl". Her powers were no match for theirs, however. Desperate, Lex sent Matrix into the mainstream universe to recruit Superman. Her efforts were successful, and Superman did aid in stopping the Kryptonian criminals, but the alternate Earth had been ruined, and was now lifeless. Superman took the orphaned Matrix, now turned into a humanoid form of protoplasm, back to his own Universe with him.
After some years with many changes to her life, Matrix was erased from existence in a forther cosmic upheaval.
