If her income is going to be that small this year then no fed/state withholding should be taken so filing exempt if not needed. https://www.irs.gov/help/ita/can-i-claim-exemption-from-withholding-on-form-w-4
Exemption from Withholding
If an employee qualifies, he or she can also use Form W-4 to tell you not to deduct any federal income tax from his or her wages. To qualify for this exempt status, the employee must have had no tax liability for the previous year and must expect to have no tax liability for the current year. A Form W-4 claiming exemption from withholding is valid for only the calendar year in which it's furnished to the employer. To continue to be exempt from withholding in the next year, an employee must give you a new Form W-4 claiming exempt status by February 15 of that year. This date is delayed until the next business day if it falls on a Saturday, Sunday or legal holiday. If the employee doesn't give you a new Form W-4, withhold tax as if he or she is single with no other adjustments. However, if you have an earlier Form W-4 (not claiming exempt status) for this employee that's valid, withhold as you did before.
