Is it possible that you feel some sort of resentment towards her, say for something she has done to hurt you or for criticizing you? Or do you harbor any feelings that she believes she is too good for you or has a higher opinion of herself than you believe she ought to have?
I would think it would hurt your wife's feelings deeply. I agree with dolfette. I don't think that you should consider exploring this fetish with her. Do you feel bad about enjoying it whenever someone says something unkind about your wife?