I assume she is not considered a household employee since you did not withhold taxes. If a taxpayer's total taxable income for the year is less than $6200, then they do not need to file a return at all. However, if you are planning to take the childcare deduction, that would mean your mother is self-employed and therefore she would be required to file a return with a SCH C. If self-employed and earned over $400, then self-employment tax (SS and Medicare) has to be paid. So while she would not pay the personal side of taxes, she would have to pay the employer side, or SE tax on any amounts over $400.
