Pragati palak's sister

Is she palak's sister or she is Shivam's girlfriend (as shivam was asking her help in trailer )

I don't think she is Palak's sister. I think she is Shivam's girlfriend. 

Palak did not have a sister. She used to have a brother. But then that brother passed away due to untreated illness when he was young. That was the reason that drove her to become a doctor in the first place. So unless a sister pops up out of nowhere then she will not Palak's sister. 

Come to think of it though. She might be Palak's sister if the Cvs will it to be. Naagin 3 showed the female lead Bella got a sister out of nowhere. Then that same sister just disappear to nowhere. Simply dusted and forgotten by the CVs. 

May be she is because in trailer she was living in there house 

Or may be Shivam sent her there 

I think she is Shivam's girlfriend. I don't think she might be Palak's sister.

I didn't see any Pragati in the trailer? Where was she?

She was there. She was the one who entered with Shivam and the empty chair and table. It seems the Noon parivaar are like empty family. The family seems haunted somehow. It's so creepy actually. 

The kids are scaring Pragati only in the trailer