First, get her into a defense-thinking mindset. Do things to make the house less of a target. Not only does this reduce the likelihood of an encounter, but more importantly, it can change her mentality. Even if you get no further than this, she is still better off.
Next, give her a transitional defensive weapon like pepper spray. Is it ideal? No. But now she is at least thinking about protection. Even if you get no further than this, she is still better off.
Third, take her to a range and shoot some 22's. Give her a chance to get used to things going bang.Even if you get no further than this, she is still better off.
Fourth, have SOMEONE ELSE, NOT YOU, give her basic firearms training. A slass, where you aren't even in the room, would be good. Any attempts by you to "help" will not help. With you not there, she can ask all the dumb questions she wants. the typical spouse dynamic will be noticeably absent. Even if you get no further than this, she is still better off.
Fifth, now go shooting bigger guns with her, and see if she wants to try any of them. Explain that the bigger the gun, the less recoil, if all other variables stay the same. The bigger the bullet, the more recoil, if all other variables stay the same. Let her decide what seems to fit. If she's happy with a .380 and you want her shooting a 357, then you compromise and get a .380.