The best way to deal with her is from afar. Many companies have employees who seem to function as little more than walking mines. You don't want to step on one, and you can get hurt even if you go near them. As long as you are not reporting to this person, try to have minimal contact with her.
Unfortunately, sometimes people in her position have a heat-seeking system that brings them into the departments. When this occurs, the best approach is to deal with her in a friendly, professional, and businesslike style. If she has a self-serving barrage of questions and answers, refer her to your manager.
The biggest mistake is thinking you can win an argument with her. Putting aside the fact that she is the owner's wife, it is all but impossible to prevail with any know-it-all. Bona fide know-it-all's will never concede that you are right, and they can drag out a disagreement with more tenacity than a two hundred pound marlin. Even if you score every single point in the debate, you will never see her wave the surrender flag.
If, by some miracle, you do prevail, one major outcome is that you will have succeeded in brow-beating the owner's wife. You may want to think twice about what you are really winning here.
If she is disruptive to your department, you and your fellow employees should consider two possible approaches. The first is to meet with your manager and point out the specific ways in which individual and departmental performance has suffered as a result of her intervention, and ask your manager to help deal with her. At the very least, your manager needs to agree to be the key person in your department to have contact with her.
Secondly, take a careful look at the owner. Is he the type of person that can be approached on a matter like this, or is such a meeting nothing but a short-cut to the exit ramp? If he is approachable, the focus should not be a tactical strike against his wife -- instead, focus on what is best for her and the company.
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