Thank you for responding.
Err.... Why avoid being a target? For the same reason females avoid dark alleys? The poor girl was very distressed by the men in cars.
She may not herself know that very many men get fetishes about schoolgirls in uniform. In those clothes, walking home alone, she is not only a target because she is visibly female, she is a brightly flashing neon sign, because she is wearing the fetishist's dream clothes, those of a schoolgirl.
You are absolutely right, that the difference between males and females can be easily detected, regardless of clothing. However, there is evidence that the difference is spotted by women, more readily than by men, presumably because women's lives or safety rely on knowing the difference, but men don't need to fear anything except another man who is far bigger and stronger. Autogynephile males often actually convince themselves, and other men, that they can pass as females.
The fetishists looking for a schoolgirl to drag into a car, and the misogynists looking for females to frighten, will be inflamed, and dangerous, at the sight of a schoolgirl in uniform.
With luck, they might hardly even notice some shapeless anonymous person, while they drive along with their eyes scanning the pavement for interesting prey.
Because they are males, they may not even spot the little tell tale signs you rightly mention, including "posture, gait, height, stance".
The lumpy grey person shambling along in a boring unisex hoodie and tracksuit trousers might be a boy, or a short man, if glanced at by a man eagerly hunting for schoolgirls.
The armour of some kind of easily carried disguise, hiding that uniform, just might be worth a try,