@bastek66 Realistically? Not necessarily.
Some people just have bigger breasts than others, if you get a certain amount fat your breasts will generally grow bigger, and then if you lost weight after that they'd probably shrink back down, but that doesn't mean any time you lose weight your breasts will get small, nor any time you gain a little bit that they necessarily changed much either.
I don't really know what all factors into breast size, but like, I have some, getting fit doesn't just take away your breasts or such.
Anyways, she's fictional too which contributes to what size they are, but they're not even breasts that someone as generally fit as her couldn't have.