Wasn't Amba having affair with a married man?So how did she expect him to support her over his wife and kids?Otherwise I understood her reasons for saying no to SaiYa wedding.They were valid.Let's see how she agrees later.
see her concern for her son is right. At the end no mother wants her child to suffer. She may agree because Satya told that if he gets married it will be only with Sai or else he will not get married that might push her