I recommend a revolver and a shotgun for home protection.  The revolver (i.e. .38 special or .357) are virtually foolproof and ultra-reliable.  If you get a new one, then I recommend taking it to a gunsmith to have the trigger adjusted for your person.  That is the downfall of the revolver... it can be a bit hard for petite or older ladies to pull the trigger, but this can be adjusted.  (Use hollow point rounds for better stopping power)