If the $100 is her only income for the year, she does not have to report it and she does not have to file a tax return.
If she is filing a tax return for other reasons, she should report it as other income on Schedule 1 line 21. Here's how to enter other income in TurboTax so that it will be reported on Schedule 1 line 21 with a description that you enter.
- Click the Federal Taxes tab.
- Click Wages & Income.
- Click "I'll choose what I work on."
- On the screen "Your 2018 Income Summary," scroll all the way down to the last section, "Less Common Income." Click the Start, Update, or Revisit button for the last topic, "Miscellaneous Income, 1099-A, 1099-C."
- On the next screen, "Let's Work on Any Miscellaneous Income," scroll down and click the Start, Update, or Revisit button for the last topic, "Other reportable income."
- The next screen asks, "Any Other Taxable Income." Click Yes.
- On the next screen, "Other Taxable Income," enter a description such as "Class project" and enter the amount. Click Continue.
- On the next screen click Done.