This is what you need to run by her....b/c it's wrong:
"But from a tax law perspective, the motivation for engaging in a business is not important."
Your business has to have a For Profit motive. Dealers can indeed deduct their TCA dues....or at least a portion of them. It's an Above the Line Deduction on your 1040's Schedule C, your Federal 1065, Federal 1120S, or whatever Form your entity has to file.
This deduction does NOT show up the Federal Schedule A of a Dealer as a Charitable Contribution. It's an Ordinary Deduction.
Regular TCA members....who are NOT engaged in a business....can not typically deduct their TCA Dues....as an Itemized Deduction or any where else.
There's another rule that says Hobby Losses are only deductible to the extent of Hobby Income.....but that's another discussion.
