X2 on the S&W. A revolver is the easiest and most foolproof handgun for a beginner. Also get her some firearms training, if she isn't VERY familiar with how to use it, she won't be able to operate it under stressfull conditions. Plus it does her very little good if she can't hit what she is shooting at. Be sure you purchase some good quality ammo to load in it for defense. Use some type of hollow point or expanding type ammo, NOT ball (full metal jacket). Ball ammo has a tendency to punch straight through and cause little damage. However the most important thing to stress is MENTAL preparedness. Winning a gunfight is in large part being mentally prepared for it to happen. Make sure that she realizes that it isn't like in the movies where a single shot drops the bad guy in his tracks. I know that it sounds silly, but many people don't really think about this and it comes as a real shock when it happens and then they don't know what to do. Make sure she is prepared to keep fighting, shoot at alternate targets (head, pelvis) to stop the threat. And most importantly, make sure that she is mentally prepared to take someones life. Sure most all of us can do it if it comes down to us or them, but if you aren't mentally prepared it can be very difficult to deal with the after effects.

DO NOT waste your time with a Taser. They are a great tool for Officers to temporarily incapacitate someone in order to take then into custody. However the key there is TEMPORARILY, once the Taser's cycle finishes the effects stop. It is not realistic to think that you can stand there and tase an intruder over and over to keep him incapacitated until the Cops arrive.