In the ending of Jumper, we got to know that David has a half sister played by Kristen Stewart. What is the significance of her role? I am not aware of the novel series from which it is adopted. Does her character have a significant role in the novel or is it just a cameo?
While I have nothing to back this up, it seems to me her character was placed there for sequel purposes. Seeing as how she wasn't introduced until the end of the movie lends me to believe they were leaving something open for further story. Just as you are questioning now, having such a character placed so obviously at the end of the movie would leave someone to ask if she might have the same powers as her brother? Those kinds of questions can help drive the sequel. They will always leave an opening to make more money. As I remember, the movie was okay, but didn't do well at the box office, so a sequel never coalesced. With Hayden Christensen's popularity (or lack thereof after Star Wars) it's no wonder there was never a sequel.