Nope. My wife is an accountant. She says that it was a gray area that the IRS almost always overlooked back 30 years ago, (and in the case of a lease as long as both parties were on it, the law didn't apply) but now, with "domestic partner" legislation, it's a moot point, even with only one person on the property deed and mortgage (although obviously only the person on the mortgage can claim the deduction.)
Your wife is mistaken snd not a very good accountant. Income is income and it is taxable. There is a big difference between simply sharing living expenses, insurance costs, or taxes (which are not income to the homeowner) and sharing the cost of the mortgage on a single family residence (which is income to the homeowner). The IRS does not take kindly when someone tries to hide income by calling it living expenses. You would have to be able to document true costs for everything, which could be a problem if you are not good at record keeping. Lots of tax penalties if you are caught earning income and not disclosing it. I would never advise someone to just ignore their potential liability on taxable income. I would advise them to know all of the legal issues before renting out parts of their home, even to a friend. They also better discuss this with their mortgage company, because they could be violating their contract. They also need to know local ordinances about multifamily homes.