Very good points everyone !! Wonderful discussion !!
I can't think of anything that has already not been highlighted before.
IMO, both as mom have not been perfect, but from what it has been shown so far, Sia has been used to take control of situation from a very young age due to the unstable character of Archana. On the other hand, Astha always was over protected by Simran and Astha has been a little in awe of Simran, the reason for which she always wanted to be like her. Astha always took Simran for granted and Simran did little to shake Astha of that, barring one incident when Simran had been very let down by Astha's attempt to pass her exams thru cheating and showed it.
Innocentindian brought forth a valid point, that what Archana did to Sia, right from kidnapping her to trying to keep her from finding her real parents by faking suicide was pure evil, a manipulation of the worst sort. Besides, Archana's motive to do so was not to protect Sia getting hurt but rather save her own skin, while Simran's effort to hide the truth from Astha generated from an intention to save her from getting hurt....