You now know why so many people are buying LCD TVs instead of plasma. LCD does not have this problem, and your wife could watch Oprah all she wants without fear of damage to an LCD set.
Basically, with your TV, you need to virtually always have a picture covering the entire screen. This means you need to distort or crop the image to make it fit. Hopefully, you have the "aspect ratio" choices in your set to accomplish this. If your wife hates both distorted and cropped images, you will need to buy her something else to watch, like an LCD or some other option.
And, as rgriffin25 says, it is a good idea to get a setup disc and adjust your picture settings with it. Basically, the higher the brightness and contrast, the more likely (and sooner) burn-in occurs.