It could be that she's been exercising less. This can cause loss of muscle mass. Muscle is denser than fat, so you can gain fat and lose muscle and get fatter without gaining weight.
If that's the case, there's only so much muscle she can lose. After that point if she puts on any more fat it will have to increase her weight.
My article "How to Get Fat" may also help. It's on my site.
12 years
