It has been far too long since I've read a lesbian-themed retelling of a traditional story. This one is pitch-perfect. Even the design details of the book (published by Little, Brown, 2009) add to the atmosphere, with elaborate drop-capitals opening each chapter and judicious use of an elegant script font for the first line.
Any sexual references are oblique. For example, when Ash asks "Will I die?" the answer is "Only a little" and then the scene changes to the next morning. I am comfortable recommending this novel to Grade 6 and up. A shorter retelling of the Cinderella story can be found in Emma Donoghue's lesbian-feminist collection, Kissing the Witch.