I don’t know if she had one tucked away somewhere. The ones she wrote about usually caused their owners a good deal of bother, but they played a big part in my childhood imagination.
Diana Wynne Jones has sadly just died, and Charmed Life is still my favourite of her books. I think it’s near perfect, it’s so well-plotted and so funny and a little upsetting, while Chrestomanci, who, if I remember rightly, possesses the ability to sweep out a room like a very long procession of one person, is an absolutely unforgettable character.
But I loved her uncertain heroes too; Cat in Charmed Life, Moril in Cart and Cwidder, Gair in Power of Three, who discover what every child dreams of – that they possess talents no one else in the world possesses; but also that such talents can bring sadness and (sometimes hilarious) disruption and responsibility, as well as happiness. She was a wise, as well as an incredibly inventive writer.
PS I’ve just found a marvellous essay Diana Wynne Jones wrote about her own sometimes charmed life here.