I'm thankful you love your wife in spite of this problem, and you genuinely want to help her. Too often, I'm afraid, someone in your situation might simply ignore their spouse's hurts, or else constantly criticize them for their reactions -- which would only make things worse.
We've all been hurt by what someone has said or done to us (or sometimes because of what they've failed to say or do). And unfortunately we've also hurt others, sometimes without even realizing it. One reason I wanted to reprint your question is because I hope it will make all of us more sensitive to the feelings of others, and more committed to helping rather than hurting. The Bible says, "Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs" (Ephesians 4:29).
What can you do to help your wife? First, love her -- and let her know repeatedly that you love her and treasure her. I'm not a psychologist, of course, but I suspect that down inside your wife suspects others look down on her -- because she looks down on herself. Do all you can to let her know this self-image isn't true. You love her just as she is -- and so does God.
Then if possible suggest that your wife seek help from a counselor who can help her understand her feelings of self-doubt. Your pastor can suggest a trustworthy counselor who can assist her.