You've provided her with a revolver whose durability is the stuff of legend and lore. Replacing it with a newer model out of fear that it will fail is rather silly. If the revolver timing and lock up are as good as you say, then what reason do you have to be afraid? The new models won't do anything that your Security Six won't do. You're essentially wasting money (unless, as has been stated above, you just want a new gun) retiring that gun in prime condition.