Spider-Girl originated as a single issue of the What If? series. In issue #105 (1998), near the end of the book's run, Tom DeFalco and Ron Frenz told the story of May "Mayday" Parker, daughter of Peter Parker and Mary Jane Watson. Both smart and athletic, May discovers her father was once Spider-Man and she's inherited his powers. This comes in handy when Normie Osborn (grandson of the first Green Goblin) makes an attempt on Peter's life, inspiring May to don a Spider-Man costume to save him.
DeFalco, at the time a former editor-in-chief of Marvel, was eventually able to launch a series of three comic books set in the universe of What If#105. It was originally promoted as "Excelsior Comics," but presumably Stan Lee himself cracked down on that; instead, the line of three titles were collectively "MC2." The three founding books were Spider-Girl by DeFalco & Pat Olliffe, A-Next by DeFalco & Frenz and J2 by DeFalco and Ron Lim. Each title was intended to feature stories designed for new readers and were supposed to have an aggressive marketing campaign outside of comic book stores so that those new readers could find them.
After the first year, A-Next and J2 ended, DeFalco intending to rotate the line of three titles every 12 issues. Spider-Girl was supposed to end with it, but it was ultimately decided to keep her series as the one firm book in the line. The replacement titles Wild Thing (Larry Hama & Ron Lim) and Fantastic Five (DeFalco & Paul Ryan) were swiftly cancelled for reasons I'm not aware of; it was almost curtains for Spider-Girl too, but it managed a reprieve.
Spider-Girl soldiered on as the last remnant of the MC2 line, a line which never achieved the end it sought. Instead, the series became best-known for being perpetually in danger of cancellation, spared in part because of online fan campaigns to save the series. Marvel had enough faith to launch two "Spider-Girl Presents" mini-series for the Buzz and Darkdevil (both DeFalco & Frenz), but then cut back. Still, Spider-Girl carried on. It got to a point where it seemed as though Spider-Girl was an indestructible title and MC2 made a near revival as mini-series Last Hero Standing, Last Planet Standing (both DeFalco & Olliffe), Avengers Next, Fantastic Five (both DeFalco & Lim) and American Dream (DeFalco & Todd Nauck) hit the shelves.
But after 100 issues, Spider-Girl was cancelled. Again, the book refused to die, instead relaunching as Amazing Spider-Girl (still by DeFalco, but Frenz had long since taken over the art) and lasting 30 issues before another cancellation. Spider-Girl moved her stories into Amazing Spider-Man Family without missing a beat; then it moved into Web of Spider-Man; finally, Spectacular Spider-Girl, a second relaunch! Unfortunately, this relaunch was cut off at the knees; Spectacular Spider-Girl was retroactively cut down to a 4 issues mini-series and the series was wrapped for (seeming) good with the aforementioned Spider-Girl: the End one-shot.
Tomorrow I'll take a closer look at Spider-Girl's publishing history, including my take on what was once a controversial subject...