Well this is an interesting development... Mal's made a poll asking if she should gain or lose weight, and how much:
http://www.polljunkie.com/NAd49Z/Poll18968.aspx
Just to be honest, I actually prefer her at her smallest in that chart. She's still has a generous body, and isn't too thin. But each person has a different opinion.
Actually in the poll right now, the option far ahead of the others is for her to become heavier than any of these pictures (that they would like her to weigh 200lbs). Then 181lbs (the heaviest picture here), then 145lbs, then 160lbs, then 136lbs. Some options list "when we last saw her" and "original weight". I'm not sure which picture depicts her now, and which are older. I had thought the story was that she had been much more overweight in the past, and had lost weight before most of the pictures posted. As she lost weight, she wasn't losing as much weight from her butt and hips and these pictures where showing the result. That in her original pictures posted here she was slightly heavier, and has continued to lose some weight. I would have thought that the 136lbs picture was the most recent, but the poll says 145lbs is "stay the same"- but that 160lbs is "last we saw her".
If you look at the set of pictures thought, you can see a lot of her weight goes to her bottom. From the smallest to the biggest, her waist only increases by four inches, but her bust increases by six inches, and her hips increase by ten inches.
Edit: TheZookie007 replied while I was writing this, so the poll numbers are probably unneeded here.