Here is my experience with stun guns, back in the late 80's stun guns were the hot item in law enforcement, everybody was getting them. The interesting thing about stun guns is that you never know how an individual will react to them, some guys it puts down, right now, incredible, others will just stand there and laugh at you, all they get is a tickle, the vast majority of the people will feel it pretty good, that's when their mental attitude takes over, it might make them mad and really start fighting, or it might make them want to stop fighting, so the results were less than stellar. We guessed at the time that body chemistry has something to do with how a particular person reacts, but keep in mind that if someone is really hopped up on something it often fails to work very well, they can fight through it.
The fad that was going on lasted 2 or 3 years then died out, stun guns weren't dependable so the officers quit carrying them. Now they are back in fashion, to the best of my knowledge the technology has not changed at all. So the effectiveness of the stun gun is quite mixed, better than nothing, pepper spray is often more dependable than a stun gun, just keep in mind some people can fight even after they have been hit by pepper spray! Neither one can guarantee your wife's safety.