The psychological defenses of rationalization and denial can be so strong as to block the truth from the person. Yet, the psychological defenses are not necessarily so strong as to keep the truth away indefinitely. Over time, a sense of guilt may creep into her story. Try to be aware of these even slightly open doors. It is at the time of even a little doubt in her mind that you can discuss what is true about stealing and what is false. Eventually, if she becomes aware, even a little, of her guilt, then you can begin a conversation about seeking forgiveness and making reparation for the theft.
To learn more, see Why Forgiveness Is Not Only a Psychological Construct.