The real question is if this was before or after the Marcus incident with Ms. Marvel in Avengers (and easily answered, it was way after).
Anyway, it's interesting that the cites that the wiki page links to viz. Equinox are JLA 105-108, which have absolutely nothing to do with power girl, but feature the end of a Chuck Austen story involving some family getting superpowers from a meteorite and the beginning of some Kurt Busiek story about the Crime Syndicate of the Antimatter Earth, respectively. Also, the publishing dates are wrong.
Only note of interest, other than Austen managed to come up with an inoffensively okay plot, coupled with his inability to write authentic-sounding dialogue for most of the characters, is that on page 12 of 105, there's one of the most epic art fails I've ever seen, where John Stewart and Wally West are supposed to be playing a video game and Ron Garney rendered nothing on the world's largest irregularly-shaped CRT, and the colorist rendered not only nothing but a Photoshop-pointillized white field on top of it. Good work, guys! Maybe the panel's catching them between firings of the electron gun... yeah, that's the ticket.
Could it supposed to be Justice Society 105-108? I dunno and my concern is evaporating.
Anyway, Equinox isn't a very good name for a villain. It sounds like it should be cool, but, unpacked, "day when the center of the sun is in the same plane as the Earth's equator" isn't exactly, oh, "Dr. Doom," is it? Outside of a henchman working for the Calendar Man, it's quite terrible.