She should be charging a fixed fee for the review itself. She has a whole bunch of things she clearly doesn't need and isn't even paid for her labour...
Unless I'm misunderstanding it's more straightforward. The article says she is reimbursed, so the steps are (based on my Aus understanding, US tax law may vary):
1) Buy product - taxable expense for business/work purposes
2) Write review
3) Get sent money equal to purchase price - taxable income
Net, the money cancels out to no taxable income but she has the product. It was bought with her own money and still belongs to her.
It's like if I run a blog, I bought a new PC to do my blogging (business expense), wrote about how nice it was, then the company sent me some money or a gift as thanks. I wouldn't have to pay tax on the PC if this happened.
In the U.S. a court would probably ignore the formality of the transactions you describe and simply look at the outcome. The outcome is that the reviewer has ended up with the property at no out-of-pocket cost, and would thus be considered income.
You're probably right. We often have the legal idea of "arm's length" meaning a transaction that is coincidental or purposeful will be treated differently.
I find this interesting in your link:
"if a transaction has no substantial business purpose other than the avoidance or reduction of Federal tax, the tax law will not regard the transaction"
I don't see how that doesn't apply to all the shuffling we see from big corps these days, licensing things they own to companies they own just to shift profits. Though that's another tangent.
