Unfortunately, this book has very little magic in it. I am thinking they can just drain the blood out, remove most of the internal organs, stuff it with wool, stitch it up, and use clay, joint compound (drywall), and fake stone composite to create a sculpture on top of the body. It would be porous, so the gases could escape, but it would also be relatively moisture-tight. Decomposition would be very slow. The final result would look like stone.
Karen brought up a scary prospect via e-mail. If I bronze her, the gases might make it explode like an old pop can.
Not a pretty sight since I am "hiding" it in the window of a pastry shop.