When Dev tells her about his dream girl and when he discloses that he is in love with the DG not with his wife she slaps him and said that he should not talk about it anymore and should think about the family's honour, happiness etc.
When the stage is set for Dev to marry Radhika she refuses to give her blessings to the relationship. Even though she pretty well knows that her son's happiness lies in Radhika and even though she loves Dev a lot, she puts forth what is written in Dev's horoscope as an evidence to go against the marriage.
Again after giving her consent half-heartedly to the marriage she keeps worrying about Dev's kids who are yet to be born.
In her logic, though Dev would be the happiest in the world by marrying Radhika, she thinks that it would be a shame on her family.
Thus going according to her logic and her nature, it is possible for her to abandon her child just because 'the family happiness' was more important for her than her own child. Though what she did is completely wrong, being 'Vaishali' she did so. Just as Radhika hid her first marriage truth to save her adopted family, Vaishali has hidden this truth to save her husband's family, because the new born was said to be a destroyer of the family.
Anyway, in my opinion it was a logical way to find a connection between Shanthanu and the Purohiths rather than trying to bring him in as an illegal child of Sr RajPurohith or Vaishali as that would raise a question about their characters. And that would have a bad reflection on Dev and his children as well.
As the precap shows Dev trying to leave the house, I think Radhika will have to do a lot of pacifying and will have to play it hard to make Dev understand that he is needed in the house to save the Purohiths from evil. And in the mean time if Shanthanu develops a soft corner for Radhika it would be interesting to watch how Dev would react as he is over possessive about his wife.
Would love to hear your thoughts on this..........