I looked for some .410 shells with #7-1/2 shot for my wife’s shotgun the other day (a shell size that I don’t reload) and even Wallyworld was out of stock on .410 shells.
Correction: Wallyworld did have a few boxes of Winchester .410 3 inch shells loaded with 3- 000 buckshot pellets in stock, but my wife keeps some .410 slugs on hand for repelling boarders.
The little .410 doesn't get much respect as a defensive weapon, but IMHO an 88 grain .410 slug at 1800 fps muzzle velocity would probably ruin a BG's entire day. Or night, as the case may be.
The .410 can be tough to find cartridges for. You might consider getting your wife a 1200 Remington in 20 gauge. The 1200 is a great shotgun to introduce newbies to the shooting sports with. It is simple and has relatively low recoil. The .410 is generally classified as an “experts” shotgun. Maybe your wife is an expert with a shotgun.