Her measurements call for a size 8 in the bust and waist, and a 10 at the hip. Since the dress is so full below the waist, I'm thinking I can disregard that measurement entirely.
One thing I'm not sure about, though, is the fabric. The pattern envelope lists Matte Jersey, Lightweight Crepe, Soft Faille and Stretch Velvet. So some of those are knits and some are wovens, right? We're thinking about crepe-backed satin for the real dress, using a combination of the shiny and matte sides.
We did pick up some inexpensive cotton to use as a muslin, but I'm not anticipating any real fitting issues, other than she is quite short and a little broad across the back. It seems like this style should be easy to fit, but maybe this is a case where ignorance is bliss.