In recent years I've become a big fan of anti seize, not only on spark plugs but on every bolt on the car. (except where thread locker is prefered) However, you have to use it sparingly. On plugs I usually just use something like a plastic wire tie to paint it onto the threaded area only, because too much can ground out the electrode, I have been told.

If the plugs were hard to remove from your wifes car you should use a spark plug thread chaser first to clean out any corrosion or carbon. If the threads aren't clean you could possibly break off a plug either putting one in or taking it out. Auto parts stores carry them and they usually have two thread sizes to accomodate most cars.

Make sure you don't have another issue and you are thinking it is the anti seize, like a spark plug gap that is not right (NEVER trust the gap on plugs out of the box, they vary greatly from plug to plug and are sometimes closed altogether) You might have also put a plug wire back on the wrong plug............we've all done that at times.

Don