...Situational awareness and managing unknown contacts from a distance all go a long way to preventing problems. Beyond that, in order of priority:
1) Good unarmed skills, preferably MMA based.
2) I know she does not want to carry a handgun, but for some situations, there is no other solution. If she is going to carry a defensive device, this one cannot be beat.
3) Pepper spray. Get one with an active ingredient having at least 2 million Scoville heat units, and preferably a 10% concentration of the active ingredient. Get a dispenser that is convenient for her to carry, easy to use, and preferably uses a cone-shaped spray pattern. This spray pattern will limit range, but maximize the likelihood of spraying the attacker's eyes at the distances at which problems are likely to occur. Recommendations include the Spitfire unit sold by Sabre Red and the ASP Key Defender. I would lean towards the former if she does not get serious about unarmed skills, and the latter if she does. Like the Taser, this is not the complete toolbox, but is one tool in the toolbox.
4) improvised/expedient weapons.
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