Satan Girl came into existence when Supergirl was affected by red kryptonite that caused her to split into two bodies, one of whom was evil. The evil half calculated that, if she could siphon off the red kryptonite radiation in time, she coulkd retain her existence instead of fading away like red kryptonite effects always do after 24-48 hours.
Satan Girl attempted to siphon the radiation into the female members of the Legion of Super-Heroes, who all turned crimson and fell ill. Their male comrades sent them to be cared for on the planet Quarantine. However, her plot was foiled by the good Supergirl, so Satan Girl ceased to exist and the female Legionnaires recovered.
