I think Mandira's plot has a deep relation to smriti's comeback.
Mihir can never go against tulsi for Mandira!!! Never!!
I think gautami was sent to viraani house by Mandira and Mihir came to know that gautami is not the real tulsi.And now mihitr and tulsi will take revenge from Mandira and Gautami.
Gautami must turn out evil for Smriti to come back. So, it is somewhere related to this plot