It all depends on body shape. I'm a size six now, but in a bathing suit I'm looking a little paunchy. Am I fat? No. Am I in shape? No. I have a close friend who is a size 12 and is in marvelous shape. She isn't fat, either.
There are a world of body shapes out there, and some people look horribly unhealthy as a six, while others look downright puffy.
I put Miss Hewitt at an eight, but an adorable eight. She could stand to do some crunches, but then, couldn't we all?