This book. I see why it took her so long to become the book that it is. 
Kingfisher, following in many ways in the footsteps of Diana Wynne Jones, has an exquisite sense of the rules of fantasy AND knows that the most absolutely terrifying things in the world are rarely the magic, but the ordinary cruelties that we do to each other. 
Which is why ordinary kindness is what matters so much. 
Also, as someone who loves the Goose Girl tale and definitely thinks it is under-told,

I cannot fucking believe you made Falada evil. I nearly screamed. It was so smart and worked so obviously well and I could not even deal. Horses and roses, Ursula. I cannot. Also, I have no idea why I expected this book to have a low body count of named characters. No idea.<\spoiler>
I loved the geese, I loved the butler, I hated by which I mean loved the evil parenting - Kingfisher is just so good at expanding fairy tales to make them able to say so much more. 
This also felt like something of a callback to Ella Enchanted, with the framework of “obedience”.