I'm not a Madonna expert, but I think she sort of revolutionized the pop music game and really pushed the boundaries of what a woman (or anyone) can do as a successful pop artist. The highly stylized image, the sexuality, the fashion, lyrical content, the music videos, etc.
I think if it weren't for Madonna the solo pop artist would just be a completely different thing than what we see it as now. The door might never have been opened for artists like that. And that's what my comment was about. I don't know, I might be wrong. Did she not open those doors? Was there a female pop act before Madonna that was pushing the limits of the genre and blending the whole image/sex/fashion/media thing (as well as making memorable tunes)?