Vanta sometimes exudes a darker, more serious energy than she means to and it's not due to her clothing. She could be dressed up as Babe Ruth or Micky Mouse and the result would be the same. It's mostly her eyes.
To paraphrase Quint from the movie Jaws she's got lifeless eyes, black eyes, like a doll's eyes. She also has a slow ease of movement like a monster who takes their time pursuing their prey. Add to this her towering stature and inadvertent 'nothing effects me' energy and you've got a cocktail of subliminal miscommunication.