Might be water retention. Might be muscle gain (although 2 pounds in 2 weeks is much much more likely to be mostly water retention). Might be that exercise makes her hungry, so she eats more than she thinks she does (although, again, 2 pounds is more likely to be water). Hard to tell without more information.

Salad and soup aren't synonymous with healthy food. You can get quite a few calories into either, if you aren't careful.