Your spouse can contribute to any IRA based on your income alone. However, it cannot exceed your joint taxable income.
You stated that you received $12K on a 1099-NEC. That's countable as income, but your deductions may have reduced your income to the point where your wife was no longer eligible.
The IRS says: If you file a joint return and have taxable compensation, you and your spouse can both contribute to your individual IRAs provided.
Roth IRAs and IRA deductions have other income limits.
Our joint taxable income is $102K (line 15, 1040)
see image below
Could this be why? If Yes, where do I look to find out why it believes my 2020 Earned Income is zero?
it depends on where you entered the income from the Form 1099-NEC. This is considered payment for services or nonemployee compensation (NEC) which should be reported on Schedule C.
If you did report it there, then as stated by @JohnB85677 your expense deductions may have offset the income to zero since the worksheet shows no earned income for 2020.
The earned income on the worksheet that is listed is from your 2019 return per the line description. If you do not have any W-2 forms, then the only earned income on the return would come from the Schedule C.
For a definition of earned income on the tax return use this link: What is earned income?
Example of using search image below.
I use the desktop version and entered it here:
When I bring up the list of forms, there is no Schedule C
On the desktop version, top towards the right, is Show Topic List. Click on Show Topic List. You will see everything available. Locate Business, click the little arrow to the left, locate Business Income and Expenses, click on the words Business Income and Expenses and the program takes you there.