Maybe Sundari's parents forced her into the marriage with MM and after coming to know that he's merely a factory worker, she decided to run away to find a better life for herself? Or it could be that she wanted to join the league of career oriented women who believed in establishing a successful career and did not believe in the institution of marriage and the concept of a family. She has stressed this many a times in those bank episodes. I recall the incident when Thamizh approached her for permission to attend the parigaaram and she furiously rebutted saying that sentiments are to be thrown away when it comes to work. Also whenever Thuls talks about her mum, the scene always shifts to Sundari. So I guess Sundari is Thulasi's mum. Lets see what the director has in mind 😊