Gauri, turned out to be Nisha, Anupam's step-sister. She wanted revenge from the Kapoor's for the whole Shiv-Ipshita episode.
Anupam tried to stop her, by saying that both Shiv and Nikhila are dead, bur Nisha was admant, and wanted to marry Samar so that she could become the badi bahu of the house and take revenge from everyone.
Nisha has promised to come back
Shivangi is Gauri, and she had a memory loss, but when she found out about Nisha, Nisha had her attacked in the hospital, and Gauri got shocked and rembered evrything.
She thinks tat Samar killed Nikhila, so is now playing pranks on him
Hope that helps😳
Yuks