The arrangement that you have with your mom would indicate that she is an independent contractor and not an employee. So if not an employee you do not have to provide her with a W-2 or pay any taxes for SS or Medicare for her.
She uses her own records to report the cash income and any expenses.
When she pays the Self Employment taxes for her net income on a Federal tax return, that pays for both the employer portion and the employee portion of SS and Medicare.
