Hilda is not a small girl in any dimension. She is tall. She is large boned. She has good sized muscles on those bones. She also stands in an assertive way that claims her space and all nearby space as her own. This is a girl who looks like a beater, in both physical mass and attitude. There is nothing passive or dainty about her.
She dresses in practical clothes, having no patience for frippery and her blond hair, while allowed to grow long, is lucky it gets brushed on a daily basis. For Quidditch and potions, she’ll tie it back, but only so it doesn’t get in her way.