If you haven't seen it already,
Ayu's interview with Rockin' on Japan might be helpful. Though it focuses mostly on the personal aspect of Ayu's artistry, I think her responses are commentary not only on her personal life but on Japanese society at the time. Also, when writing her Wikipedia article, I found
this New Paper article really useful (it's about her "merchandise empire".) In addition to the TIME article,
this Web Japan one also provides some insight to her influence outside of music.
And there's always Wikipedia. (It's a featured article, so it's not a repository of junk dumped there by a rabid fan/anti-fan. You can see the sources for yourself.) *cough*