First thought
I think she forcebly says yes because of all that happening with press. She might want to keep her parents out of it and not being bothered. So she may say Yes to marry. But purab may say that he does not want to marry jassi like that and then the love story will actually begin
Second thought
Jassi agrees based on what is happening with press and to keep her family with any trouble she may say yes and marry purab. After marriage she may say to purab that they are just friends and she never thought of him like that and she married him for her family's sake...
Both cases I think she is marrying PURAB!!!
I posted my opinion...
http://www.india-forums.com/forum_posts.asp?TID=1974&PN= 1