I'll assume she doesn't pay a dime in federal or state taxes. The child tax credit will return all her federal, state, Social Security and medicare with holdings and give her an additional amount just from the bottom of tax paying Americans hearts.

And the government knows exactly what social she is using. It is on her W-2 form and required to be entered when filing taxes on the W-2 information sheet. Her IRS issued ITIN is directly linked to the social she is using to work.