I'm not sure which one they meant, to be honest. I dedicated Books of Magic to Diana (and three other witches), she dedicated Hexwood to me, whereupon I wrote a poem about it which you may be able to find by searching for her name on the search function (as I put up on this blogger a while ago). She put me, as me, on a panel at the convention in Deep Secrets, and gave a breakfasty thing that had happened to both of us to a character in the same book (I was the one who ate the breakfast in question. Not a morning person). I got her a griffin for her birthday last year. My family flew on a plane to Minneapolis with Diana once, and I got to experience her famous travel jinx at first hand. Diana told me a couple of years ago that I was the first adult who wasn't either a teacher or a children's librarian to tell her, back in 1984 or 85, that I loved her books, which still makes me happy. I started reading The Magicians of Caprona to Maddy tonight. Pick any answer or none.
More info on Mr Miyazaki's film of Howl's Moving Castle at http://nausicaa.net/miyazaki/howl/
And the best Diana Wynne Jones website seems to be http://www.leemac.freeserve.co.uk/ at which she answers questions and is generally spiffing.