The bust, waist, and hip measurement difference between a 2 and an 8 is supposed to be 3 inches each. Going "up a size" is supposed to be a difference of exactly one inch. The vanity sizing issue is mostly present in department stores and particular chains. I get all my work clothes from Ann taylor loft where a 0 is a 0. I tried the JC penneys junior work line and found a georgous cheap ass suit dress thing, but the smallest size they carried (a 2) fit me like a goddamn 10. So her 8 and the 8 you're thinking is probably more like a 16.