I did this at Charlotte a few years back, 40 laps. Stay on your instructor's car's butt. If you keep up with him he will continue to go faster. Also, remember that your depth perception is severely messed up at those speeds. You may think you are 3 car lengths away from his car, but you are probably 15. They will wave you off if you get too close. I got waved off quite a few times!
You will absolutely love it. And your wife is in for the ride of her life. I did the 3 lap ride along before I drove, and my driver was Jimmy Kitchens....he got loose a couple times coming out of turn 4. Amazing feeling, will give you a brand new perspective on what these guys do every Sunday!