If your mom accidentally claimed you a dependent when she was not eligible to claim you, then she can cash the check. As long as the amount owed to the IRS is repaid by April 18th, 2017 she will not be charged any overpayment penalties. She can pay the IRS by either sending a check or paying the IRS directly via their various payment methods on the IRS website.
Please note that 1040-X cannot be e-filed - she will need to mail a paper return. It takes the IRS up to 16 weeks to process amended returns. Also, depending on whether the changes affect your numbers, you may also be required to file an amended return with your state.
