Suchitra would have continued the way if Dev was also submissive like her. Never questioning the evil trio and just went about what she has been doing all these years. Support the school, do charity, stay in US and never cross evil trio's path.
Suchitra tried to reign her son much. Directly as well as indirectly. But in the name of a girl called Nithya and whatever happened to her Dev chose to finally ignore that reign and listened to his heart. Finally he confronted everyone with accusation that Payal was raped. He directly crossed evil trio's path endangering their very existence.
Suchitra now saw what is the effect if her son stood up for himself and questioned the rights and wrongs of the family. Family simply donts wants him or her.
So finally she choose to stand for herself. I guess Durga and Dr Dayal helped in a way for this as she has moral support now.