1. Lessons in situational awareness.
2. Evaluation of her willingness to use a weapon.
3. Evaluation of her potential skill with a weapon.
4. Decide what to get, with her.
5. Train.
6. Follow up.
Before you decide what to do, you have to figure out where you are. Most people go through their entire life in condition white, and only move to orange when they should probably be in red. This is often followed by an express trip to black. The absolute best thing that you can do is get her clued-in on her surroundings, potential threats and potential counters. If you do that successfully, chances are the whole rest of the "solution" will not even be needed.
Tasers and mace are good ideas, but is she willing to use it, willing to practice with it, and willing to carry it in a way that she can access it? Most of the time people use it like a security blanket. "Well, I sure was scared, but now I have my *insert weapon here*, which I carry in the bottom of my purse/leave in the car/leave at home/usually carry but forgot it today/have no idea where it is ATM, so Now I'm Safe (tm).
Generally, I'd go with a mace over a taser, for the following reasons:
1. Easier to use.
2. Easier to carry.
3. Repeat shots for most cans.
4. Cheaper.
5. Less legal hassles (will vary by area).
Tasers get the nod for being instantly effective, which is something mace is NOT, but require more skill and dedication to use effectively.
But, address the software problem first, before you address the hardware problem.
Mike