Ah, but he’s salaried, which makes me think that this is a regular job for the OP, and an annual temp job for the Wife.
My vote for document, document, document, - write her up whenever legitimately possible, and if necessary (i.e. boss throws a shit fit) go over his head to TPTB.
But writing up the bosses wife complete with mountains of documentation gets him…what? So he can fire the bosses wife? So he can prove to the boss that the wife is a problem?
That’s not going to work. He’s never going to convince his boss that the boss’s wife is a problem. He’s never going to win in a contest between him and the boss’s wife, unless he starts providing the boss with a better class of oral sex than the wife does. The sooner he realizes that there’s absolutely positively nothing he can do about the boss’s wife, the happier he’ll be.
So, given that there’s absolutely nothing he can do about the boss’s wife, what SHOULD he do? Collect his paycheck with a smile on his face. If the wife makes managing the store impossible, then watch as the store goes down the drain, and collect your paycheck. Because you can’t fix the problem, the problem isn’t the wife, the problem is the boss. The solution isn’t to search for some way to fire the wife, the solution is to fire your boss.