Yes. A 15-year-old girl should carry anything permissible and that she feels confident using. I’ll guess that at 15, her options probably range from a pocket knife to collapsible baton or pepper spray.
Of course, permissible limits to where she is and what rules apply. If she’s going to say that criminals don’t follow the rules because they’re criminals and will carry whatever they want anyway, I agree. She’ll just have to weigh the risk-reward of her situation between protection against violence versus protection against legal action.
In addition to carrying a weapon, she should realize that everything is a weapon. She should carry several friends with her, a cell phone, sobriety, awareness, alertness, mindfulness of likely threats, backup transportation, a quick exit plan, several contingency plans, a well-rehearsed set of responses to the threats she’ll most likely face, and her dad and his friends carrying weapons.
It sounds overboard, but hey, I have a 15-year old daughter. I want her to have every advantage in coming back home to me. If she’s not allowed to carry a weapon, I’ll carry it for her. And if I’m not allowed, a real dad would carry anyway to do everything he can to protect her.