The .410 is a short range affair, always has been. So as long as your mom undertands that and is willing to stick to shots 20 yards or less, buckshot would be an effective deterrent. Ditto for slugs. A youth size single shot .410 with sling swivels and an ammo-cuff on the stock with slugs and buckshot would work well, in my opinion. I've had good results with Federal Premium Handgun 2 1/2" buckshot, here's a link to some very helpful info:
http://410handguns.com/410_federal_ammunition.html Good Luck!
Scott B.
p.s. I would probably fall in the ".410 tinkerer" category:
A pattern test from a year ago:
patterning buckshot:
Saturday, February 18 2012, sunny 30 degrees, gusty cross wind
Marlin model 200 .410 shotgun, 22" cylinder bore with 1x20 scope
Standing, one round at ten yards, one round at fifteen yards
Federal 2 1/2" personal defense 000Buck, 4 pellets
24"x24" cardboard with 3" orange dot for focus, wasn't expecting such good results...
Determining where buckshot hit in relation to crosshairs, for close in woodchuck elimination
All eight pellets in a very tight pattern, very happy!
Tried a couple other 3" buckshot loads, wildly innaccurate even for buckshot.
This round has patterned very well in my Mossberg 500 and an old bolt action .410, I like it!
Six shots @25 yards from my backyard shooting bench, scoped .410 Marlin 200:
Last woodchuck of 2012, Remington Slugger at 45 yards all i could see was his head/shoulders:
