She has enough Federal income tax withheld from her wages and paid over to the IRS to cover Federal income tax on her wages.

FORBES: IRS Expands Availability of Innocent Spouse Relief

If an employer intentionally misclassifies a worker, the employer is liable for the full federal income tax that should have been withheld, plus 100% of all Social Security and Medicare taxes!

FORBES: Worry Over Worker Status Isn't Crying Wolf

It is very similar to the money withheld from your pay for federal income tax.

FORBES: Executive of Bankrupt Airline Liable for Millions in Excise Tax