Is Chemotherapy Advisable Post Mastectomy?

Hi ,this is diba My mom had a surgery 20 days before. She is 76 years old. Dr removed all breast . Tumor size was 1.2 cm.Nipple and skin and lymph are free frome tumor. TheEr is negetive and Pr is negetive. We are in Iran we confuse 2 dr says she need chimical 2 says she need nothing would you please help me she need something or not?