Harrington & Richardson Arms Co. .22 Special. 9-shot, double-action / single-action revolver.
Best I've been able to come up with is that this model was last produced in 1943, and this one was from around 1941-42. Shoots well but has a strong yet smooth double action, the single action is crisp and clean with no movement that I can feel. And lets face it, 9-shots of .22 LR, HV hollow point is more than most people want to buck, especially considering that Mom is a crack-shot.