@nutmeg..your post definitely gives thought to ponder about..
Rightly said shivangi will create problems for Nimrit in future..
Her entry in Agam.Nimrit life will have its consequences..its not just she is here to help Nimrit and then once her job done she will go away..of course there is more to unfold about her character..
Shivangi is on a mission and by precap the way she was adamant to go means her mission is the upmost priority..
one option... Amrit might be sooner or later find out about shivangi.. not to jeopardise her mission she may side up with Amrit.
second option..As you mentioned Tej gave her the CD to learn more about Nimrit .Tej is already confused how two people can have same face..we do know he is in charge of this terrorist mission..may be Tej will find out about her reality and her mission.so to protect herself she may claim she is real Nimrit esp if she learns every mannerisms of Nimrit...
There is certain scene and dialogue that when we analyse already hints about the future track.like Shivangi telling Nimrit what if your husband really thinks i'm his wife..Nimrit telling her our relationship is more of the heart not face..time coming i will prove to him i'm his Nimrit..My POV Nimrit has a lot of fight ahead to prove to Agam she is his Nimrit..