There was no point in Shefali's Mom saying anything. In fact when Arjun said that whatever Shefali said is not correct, I would have wanted shefali to also just leave. I mean what's the point of pleading and expecting anything from Arjun at that point??
I have 2 different take on this-
First, if she loves Arjun, she should know what he is capable of and what not. So at the first place she should have not even told that they love each other in a situation where Arjun's father has attempted suicide and there were like tons of people around. What was she expecting from Arjun or anyone??
Secondly, if the person whom she loves, doesn't have guts to stand up for her now when he had promised her to do so, how that person is going be a good partner in future??