The 5.56 has less penetration through house walls than pistol bullets, buckshot or slugs.

Your wife will be safer and more effective with an AR than a shotgun. Why...?

Yes.
1)Easier to place precise shots than a shotgun or pistol.
2)Much lower recoil than a shotgun.
3)Faster follow up shots.
4)Better capacity.
5)Easier to reload or clear malfunctions than a shotgun.
6)Good terminal performance even with FMJ ammo.

MistWolf,

Thanks for the response.

Can you please provide video evidence (youtube, etc.) that proves with visual evidence using an AR15 with XXX ammo will not penetrate through multiple sheetrocks?

I have clearly seen youtube videos of buckshots for shotgun not penetrating house walls. Nothing for AR15 yet.

Check out Box O' Truth for tests with shotgun, pistol and AR rounds through drywall.

It's not that I think the shotgun is a bad choice for house defense, it's just that the advantages of the AR over the shotgun are overwhelming.

Thanks MistWolf for the comments.

I definetly agree AR would be better over a shotgun, but not at the risk of me going to jail for harming or killing my neighbor. I am curious to what ammo they used during the test with that shotgun.