My gunsafe has an electric keypad, with a factory 4-digit combination you cannot change. Another combination can be programmed for the user (myself), and a "guest combo" that can be easily changed.
If your safe has this option, simply program a "guest combo" for you wife and live at peace with yourself. If, down the road, you suddenly want to prevent access, you simply change the guest combo.
That's all I can think of, but you need to have the electric keypad and the combo options I guess for this to work for you.