I feel the theme of "The Lady, or the Tiger? is one of making the right choice and overcoming jealousy and pride. The Princess holds the fate of her lover in her hands. She knows what is behind each door and that her lover will be looking to her for the right choice, which is life. The princess feels that her lover has betrayed her with his flirtatious airs around the maiden behind the door. She knows they have spoken and exchanged glances. She also hates the maiden because of this and would love nothing more than to see her lose her lover and end up with no one and very unhappy. She also doesn't want to see her lover married to someone other than her. With all these situations and knowing her inheritance is "semibarbaric", one would think she would direct her lover to the wrong door. But if she truly loves the man, she will overcome her jealousy and make the right decision and want him to live even though the consequences would not be in her favor. She also has to not let her pride stand in the way. She feels betrayed, but she still needs to make the right choice.
Reference: The Language and Literature Book by McDougal Littell