That would be a question to ask the employer. What did she put on her W-4 at work? Sadly, there is nothing to do about it for your 2021 return, but going forward she needs to change her W-4 at work and have tax withheld if she is a W-2 employee.
https://ttlc.intuit.com/community/tax-topics/help/what-to-know-about-the-new-2020-irs-form-w-4-emplo...
https://www.irs.gov/pub/irs-pdf/fw4.pdf
https://www.irs.gov/individuals/tax-withholding-estimator
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
