You remember in 316, Jack, Kate, Hurley, and Sayid were sent back in time but not Sun and the other passengers on the plane. Since it has been confirmed that Jack, Kate, Hurley, and Sayid are four of the Candidates, it now makes sense to me why Sun wasn't transported back in time with them. Because Jacob (who I think was the leap to the past) could only transport the Candidates to that point in time and not non-Candidates who he thinks wouldn't serve a purpose even if they were sent back in the past with Jack, Kate, Hurley, and Sayid. So I think the Kwon on the list of potential Candidates is actually Jin, not Sun.