The results of that NPR poll of the top 100 SF&F books/series are now in. You can find them here. There are 15 books by women in the list, so 15%. Is that good? I suspect not. After all, this is an SF&F poll, and fantasy is supposed to be “women’s books”, except when it involves lots of hacking and slaying, of course. A total of 60,000 people voted. There’s no indication of the gender split in voters. (As I recall they didn’t ask.)
Still, there are two SF books by women in the top 25. They are by those well known women SF writers, Mary Shelley and Margaret Atwood.