First, I'd like to point out that neither option "A" (AR style rifle) nor option "B" (870 in 12 or 20) is a one handed proposition. Dialing 911 would be the next step after mom gets the gun ready...... hard to do holding a long arm.
So did you offer to take him shooting? Steer him to a class? Point him to TFL and your State Gun Owners/2A website?
then I asked to be sure if he's ever had a gun. He said no but he needed one for home defense.
Though I have always been around guns/been a shooter, I remember when I first wanted to get into reloading ...... I found that people that reloaded, (including those who were in the business of selling reloading stuff!
) were often less than helpful to a noob getting started (they would rather argue about the differences between .223 and 5.56 at the counter with their buddies, or sell Elmer his semi-annual order of 7 1/2 shot and primers than answer noob questions about what I would need to start loading my own ammo ..... those were pre-internet days, and I am so glad for TFL and other forums.
So, How many noobs have YOU taken to the range lately?
Fight Ignorance: Teach somebody something.