Answer: Form 843
Explanation:
As a taxpayer, Mary can use Form 843 to claim a refund of her Social Security taxes. First she tried to obtain the refund through her employer and should this fail, she should fill out a form 843 and submit it to get help on the claim.
The form can also be used to get an abatement on FUTA taxes as well as a refund of interest, penalties, or additions to taxes.