In the state of SC does an employer have to provide a private room for a mother to breast pump if the employer has less than 50 employees

Federal law governs in S.C. The applicable federal rules do not depend on number of employees but rather are governed by revenues, relationship of the employer to interstate commerce, and the classification of the employee as non-exempt. An employer is only required to provide a private room if it is "practicable" to do so. See http://www.usbreastfeeding.org/Default.aspx?TabId=188.