Hah! I just in the last ten minutes read a review of the Andrews biography and was going to post a link here.
https://www.theguardian.com/books/20...box=1643673507
Disclosure: I didn’t read and love the books as a girl and when I read the first later on out of curiosity, I thought it was both dreadful and disgusting. That said, the biography sounds both sympathetic and reasonable; I can’t imagine that a fan wouldn’t gobble it up. But it also has to be noted that the biographer made a very good thing out of writing as Andrews; that’s a ridiculous number of follow-on books.