I've had the nova stun guns issued to me at work. They were mostly ineffective because of the level of electrical input and the distance between the probes. The best use I found for my nova was to keep dogs away, as the sound scared them.
Having been hooked up to the Tasertron (now defunct) and the Taser X 26, and having seen them work on the street, I believe that the taser would be a better idea for her. it shoots the straightened fishhooks as darts (5 yards for some cartridges and 7 for others) to transfer the voltage across a wider area, can be used as a handheld unit (drivestun mode), and leaves you feeling like you've gone three rounds with Tyson. you don't have to leave the stun gun behind, because once you've stunned the assailant, you take it with you for the drive stun.
its not a cure all, but I'd rather be peppered than stunned.
Davidsons has the civilian Taser for sale. Any law enforcement trainer thats certified in the taser can train your wife how to use it.
Don't get me wrong, I would think that a Kahr MK9 with Ranger SXTs would be ideal, but this is a good intermediate step. A lot of agencies that have gone to Tasers do the community demonstrations of the effectiveness, if you check around you can probably get a demo done.