All she can do is ask her employer for a corrected W-2.

Box 1 of the W-2 is (suppose to be) what she was actually paid. The "assumed tips" are to be shown separately in box 8 of the W-2 (allocated tips).

As it stands now, the IRS will expect her W-2 to be reported as issued.

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the IRS has instructions on what to do if you receive an incorrect W-2 and the employer is uncooperative: https://www.irs.gov/faqs/irs-procedures/w-2-additional-incorrect-lost-non-receipt-omitted/w-2-additi...