thoughtful post Shruthi. Yes I was expecting this from Mandavi and she did run to her mother in law to support her, to console her and to lend a shoulder to cry on and empty her heart. she had seen her MIL collapsing and had seen her loosing the wish to even live on. She had seen her MIL deciding to take away her life out of dejection and regrets. Now she knows that she is the only one who can support her and bring her out of her apathy.
Moreover, kausalya & Sumithra are together and are capable of wiping each others tears and even though they are cordial with kaikeyi, it is not so easy to erase the ink completely and make it white and spotless. even though the other queens also, lost their husband and kids are away, the loss of Kaikeyi more than any one else. She not just lost husband and a son, but she lost her whole family. She lost all her 4 kids and sisters and DILs. At this moment, she was badly in need of a person who could cajole her, hug her and cry with her for her and on behalf of her.
Now that Ram Lakshman & Sita are away in forest and Bharath is on the verge of leaving Ayodhya and King Dashrath is dead, all they have is RajGuru Vashist, Minister Sumathra and Shathrughan. They can't expect any support with regard to ruling from Bharath at the moment as he is still burning with self hatredness and Shathrughan alone can't shoulder the whole burden of ruling and ecision making. They need a matured adviser and neither kausalya nor Sumithra are trained in politics. So the nation needs the service of experienced queen kaikeyi and to have that service, she has to come out of her grief and even if it has to be done as prayashchith, she has to start working as an adviser to the youngsters to take care of the state affair rill such time, Ram returns.
And about Mandavi not following her husband I n the name of patni dharma is not something odd. Patnidharma is not just to be with her husband physically. A mand needs his wife to support him morally and lend her shoulder to pull the life cart and mandavi and Urmila are doing that. Their husbands had to go out to perform their duty and wives have to take care of their other duty back home.
even today we can see the husband working in some other city or country while the wife will be back home taking care of his parents and kids. That doesn't mean she loves him less or forgot her duty towards her husband, but she have to stay back to take care of the elderly people and also the small kids. In some other cases, while the kids are in school, not to disturb their studies, mother will stay back with kids while father will be staying away alone. That doesn't mean he love his family less or the wife doesn't care for her husband. Sometimes, they have to look into others also and not just the two of them.