There are girls in there that gain weight and you bump into other girls working out in there that are gaining weight too. I think your character may be able to lose weight using the gym
Really only one way for Aubrey to get muscular, one of the experiments with Tiffany, and it's temporary.
There's quite a lot of content at the gym and Aubrey can also lose weight there if you're trying to go back to a previous weight stage or just slow your progress to a later one.
