She needs to train with a firearm and without a firearm to defend herself. She also needs the mindset to do what she must. Hardening the target is also equally as important as it is difficult to harm a person you can't get to in the first place. There is no impenetrable barrier but making a person take time to reach your loved ones is important as the police will have time to arrive and the wife will have time to react.
In my home there are a minimum of three doors a person would have to penetrate in order to get to the bedroom. Each door is hardened just a tad. Our plan is to retreat to the bedroom if we sense trouble and call for help. We both keep a handgun on our person or within arms reach at all times. There is a shotgun in the bedroom. All of the exterior doors have deadbolts, knob locks, and braces like the one in the link
http://www.brickhousesecurity.com/pr...FcSj4AodPGcAyg .
Those take a good while to break in I can tell you from personal experience (there was an issue where I heard screaming and dog barking from inside the house when I came home. She usually leaves the brace up if she gets home from work first so I had to break in through one of my doors only to find the dog and the fiance screaming and freaking out over a large bug lol.)
Basically by the time he is in the home she and the dog can be behind two other doors with 911 dialed and shotgun trained on the last barrier. If he breaches that well its time for buckshot I suppose.