I'd suggest a Taurus Judge, but if handguns are off the table due to age constraints, then possibly a 410 or 20 gauge.
Wouldn't worry too much between 00 Buckshot, #2, #4, or #7, though the larger the shot the higher the probability of lethality.
Short barrel, improved choke for max spread, and it's on like donkey kong on roids if something goes bumpity bump bump in the night.
I used to give my girl my 12ga 870 loaded with a "specialty" load, along with her 380, while I checked it out with my 45.
She had her cell phone, I had mine. She got the ALL CLEAR before I got anywhere near the bedroom too...