if she will not "carry" at home, what about this...
if she can shoot a shotgun, then she should be able to shoot a 4" barrel revolver loaded with .38 special ammo.
my mom was 78 yrs old and could shoot my smith model 19 with standard
.38s all day.
as opposed to "carrying" one, you could get a couple of blue steel used smith model 10s at a gun show and keep each loaded in areas of the house where she stays or just two good locations (maybe one in kitchen and one in living room).
These weapons can sit in a gun rug in a drawer and can be quite handy.