Did she get a W2 for it? If she got a 1099NEC or just cash that is self employment income. Even though she didn't owe income tax on it she owes self employment tax. Did it fill out Schedule C for her income? About 350 would be the right amount for self employment tax.
Self Employment tax (Scheduled SE) is automatically generated if a person has $400 or more of net profit from self-employment. You pay 15.3% SE tax on 92.35% of your Net Profit (If it is greater than $400). The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare. So you get social security credit for it when you retire.
