Mousse tends to do the least amount of bulking out, but she does like working out simply for the bonding exercise, though excessively so not so much unless she has to keep Parfait in check or if she is feeling rather down and wants to feel "important", by making herself feel "big".
Mousse as I said before, isn't much for talking, but she is nice and gentle, and while she prefers small crowds and friends, it doesn't mean she can't interact with strangers. If people were nice enough to ask her to flex for them, she would be happy to oblige, though she would still be shy and cute about it, not so much embarrassed, but feeling nice about herself that people like her body enough to want to actually see her flex it.
She has actually been getting a lot of attention at school lately from the boys just because of how approachable she is, not as rowdy and rough as Parfait or as unattainable as Eclair, and boy's like the sweet, gentle, cute girl they can easily handle and mold to their liking, which could be a bad thing for Mousse, considering how agreeable she is to a lot of things and how nonaggressive she is towards people.
All she needs is the right guy to treat her right... maybe someday she will get someone like that, especially when she blossoms into such a fine young woman.