The S&W 442/642 is a great concealed carry gun but it would be a poor choice for primary home defense weapon. There's no need for the super small grips and short barrel in a home defense situation where the gun doesn't need to be concealed. The DAO, internal hammer is outstanding for concealed carry but wouldn't be ideal for an elderly person.
Blackwater makes a very convincing argument for a 20 ga, side by side.