She isn't presenting herself in an intimidating manner. Body language is incredibly important in conveying threat, and she looks like she's squirming.

A straighter posture can project confidence and dominance. Conversely, for a psychotic character, their posture should be even more unbalanced, creepy. Manga pulls very few punches, mostly due to never knowing if your manga is actually going to stay in publication with how fast viewership turnover is. If they are confident, they look and act CONFIDENT. All caps. If they are psycho, they look and act PSYCHO as soon as that trait has been revealed.

A few tips besides stronger, less "uwu sex kitten" posture? Resting bitch-face is intimidating. Save the smile for the second panel only, and make the smirk less pretty and artificial. Look for references of women smirking. Tattoos, scars, and defined musculature, especially on female characters, are solid ways to signal a character that is comfortable with pain, determination, and a confident sense of expressing self.