Women could get to #1 on alt rock airplay around the Alanis Morissette boom (includes Hole and Garbage, and maybe Cranberries before that), and then again after Lorde breaks through in 2013. Both of these booms get integrated completely into the pop charts a few years later.
Women were at least well represented as legitimate Rock at the height of things, but if you look now, that stuff isn’t given the same canonization. Heart, Hole, Pixies, Veruca Salt, Sleater-Kinney, etc., etc. were as interesting as everything else. Riot grrrl scene was big here (in Seattle).
What I think is interesting is that there are times where this DOES tip over into legitimate radio channels, but these moments have historically been short-lived and the ensuing reaction has sort of razed the landscape: once in the 2000s (for the whole decade!) and again now
I think what Rockists look for is a band. They think of Alanis and Taylor Hawkins and that’s built into a legacy they understand. When they think of Lorde etc. it doesn’t match what they expect and relate to their male-centric canon. I do prefer a band too re Rock music, but that’s preference.
My line going way back was that single-name-performing-artist *is* usually a band (often a pretty consistent one) and is usually more about marketing than approach. (And by contrast men leading "bands" in name only.)
Heck, even archetypal solo pop artists may be bandleaders of sorts, just most often a changing and/or electronic one (late-career Madonna the ur-example here, and Tom rightly likened her to James Brown in her highly conscious collaboration shifts)