I did not get a good vibe from this maasi character.
I feel it could be two things:
- she was infatuated with jaggu even though he was married to her sister. One night she gets him drunk by mixing something in his drink and then sleeps with him pretending to be her sister. she then gets pregnant and blackmails jaggu. Now pratibha also gets pregnant. jaggu refuses to leave Pratibha and decides to tell her the truth. Mami knows that her sister will forgive jaggu and gets them into an accident. Both mami and pratibha need to have emergency premature delivery. Jaggu tels mami to leave and never show them their faces. Now the twist could be- mami loses her baby and pays the nurse to swap her and prathibha baby( prathibha will be karan's real mom). So now it looks like mami's child survives. Jaggu will be devastated. Mami tells him that he needs to support her financially and she will give her baby to praibha. Jaggu won't agree but when he sees his wife go hysterical he agrees. For a couple of years after that mami will frequent the house and try to make it seem that she has done such a favour for jaaggu. Finally jaggu kicks her out and tells her never to come there again.
So now the track will be that she has come back to take Karan. Jaggu will get mad and tell her that Karan is only his and prathibhas son. Karan will be confused and ask jaggu and dadi for the truth- since they still believe the lie mami told them years back, Karan is devastated and decides to leave sb because his blood mother wasn't treated fairly. Abha will support him but events will occur that will make her suspicious of mami. Abha will uncover the Truth and finally everyone will come to knw that Karan is really pratibha son.
The second scenario can be that mami is not really mami and is there to cause problems because of some old rivalry with jaggu