If Sia really cared for Aastha she would inform her parents of her lies and try to bring things out in the open so her family can resolve things TOGETHER and heal.
But no, from Sia's actions, it looks to me that subconsiously she is letting Aastha get deeper into trouble and alienating her more from her family.
Sia needs to examine her real motives and priorities - maybe she just likes to be the 'good one' in the family. If Aastha become good then no one will pay Sia any special attention....
What do you think?