I believe if you paid her less than the cost of the expense (which is the only way this would benefit you, tax-wise) then it'd be a red flag - it's not really part of her "business" as it's clearly just a tax game and would certainly look sketchy to the IRS. If you paid her more than the cost of the expense, you'd be worse off (creating net income for her with after-tax dollars from you, notwithstanding the tax deductible expenses). If you paid her exactly the cost of the expense, you'd be (as a couple) neutral, but would have gone through a lot of trouble for no reason.