A few points that should be obvious, but don’t seem to be!
1) Most girls of shidduchim age do try to be as attractive as possible. However not everyone is built the same way, and not everyone can be super thin! There are many medical reasons besides the few mentioned that prevent girls from being a size 6 or below, and even perfectly healthy women come in various sizes. Being heavy is NOT an automatic indication that one doesn’t care about how she looks, or one does not have self control, or is not healthy enough. Two individuals who eat the same food and exercise equivalent amounts may look very different. The judgmental tone of so many posters is very disturbing.
2) Body shape changes throughout life for everyone, and especially for women having kids. A previous poster discussed her experience loosing weight with her pregnancies, and actually that is not so uncommon (I had the same experience and researched it a bit). Actually heavy women as a whole gain significantly less weight during pregnancy than very thin ones. A woman’s body is programed to store fat during pregnancy (specifically on her hips) in order to provide nutrient sources while nursing. Someone who already has those stores tends not to store as much new fat as others. Just like the poster, I lost weight in the initial stages of my pregnancies, and then gained back only a bit more then I lost, which was less than the weight of my babies! Of course the genetic and metabolic factors that enabled a woman to be super skinny to begin with may work in her favor and help her loose the baby weight faster, too. Bottom line is to keep this weight concept in perspective: it is a very superficial characteristic of a girl, and a transient one at that!