The key here is that the founder's wife has a regular presence in the office. Plus, a founder is in a vastly higher position of authority than an employee (be it a manager, or else).
So it's not too far to imagine that she could exert some influence towards her husband's decision at work, e.g. hiring and firing of someone.
I hire people, and I talk to my wife all the time about work matters. And if, knowing everything she knows about my team, she told me that I should be looking at cutting someone loose, I would take that advice very seriously. Every good executive has trusted advisors, and for people in serious relationships the partner is very commonly one of those advisors.
The only problem here is the wife's alleged direct meddling with work matters, not that she had a strong influence on her husband's work decisions. For founders, life is totally enmeshed with work and it would actually be weird if his wife DIDN'T have strong opinions on the company he built while she supported him at home.