DHARMESH-VAISHALI-MADHURI:
Archana's youngest sister, Vaishali, was married to a fat rich guy Dharmesh and was with child with him. It was discovered by Archana and Manav that Dharmesh had a hidden life with a first wife and child who had some disease. He visited her in Pune frequently and lived as husband and wife. He was also attempting to make another child with Madhuri so that their child Varun could have bone marrow. So anyways after everything was found out, Archana co-hearced Madhuri to court to make her marriage not valid in court so that her own sister Vaishali could get the title of legitimate wife, and her child get Dharmesh as a father. In the end Vaishali got custody of Dharmesh's first child with Madhuri as well but Vaishali treated the child poorly. Dharmesh also abused Vaishali quite a lot. But Archana "fixed" everything.
Now it'd be interesting to see if Archana takes the same approach with Onir-Shalini-Purvi. One thing we know is Onir isn't rich as Dharmesh was so maybe that might affect Archana's decision. Also, if Archana can send Vaishali to an abuser like Dharmesh, I don't see why she won't send Purvi back to Onir. She would be a hypocrite if she doesn't, meaning she cares more for her daughter then she ever cared for her sister