Contemporaneous Roman descriptions of her, which was NEVER flattering, never mentions her height, doesn't call her plump nor obese, but do talk about her charm and intellect, as well as her being cunning.
Coin depictions of her do not portray her as fat and neither do they make her look like a beauty.
Charisma does not depend (totally) on physical beauty although it helps. Two Romans who were no dummies and no mean shakes in the charisma department fell for her.
She probably did not have the figure of a teenager by the time she died but as she was a mother several times over that would not be unexpected. As for fat, probably not.