Rupert goes to vote. He votes for Rob. "I don't know what else to say; I hope we both have two votes, and I hope we go into a tie." ["The fact that he wants there to be a tie in which someone who doesn't get any votes could go proves exactly why he never could and never should win this game." -- Wing Chun] Rob votes for Rupert. "You're a gentleman, buddy. It's been a pleasure playing the game with you. I hope it's you tonight and not me." Amber votes. Jenna walks up to vote, and seriously does seem to be waffling even as she holds her pen over the paper.
This is how I see Jenna's choice: Jenna has exactly one way to win, and that is to make it to F2 with either Rob or Amber and hope the jury is really bitter and petty. And because Rob and Amber will take each other if it comes to that, this requires her to win the final immunity challenge. Therefore, Jenna cannot win the game without winning the final immunity challenge anyway. While her chances of beating Rupert and Amber in that challenge might be marginally better than her chances of beating Rob and Amber, I don't think they are so much better that it justifies taking a one-third risk of being eliminated at this stage. In other words, Jenna's got to bet on herself at the F3 challenge, so once she's done that math, there's no benefit in risking the rock. To the degree that she hurts herself with the jury by booting Rupert, she's going to have to do that at F3 anyway if she wants to win. If Rob goes now and Jenna wins F3, she'd have to take Amber instead of Rupert if she wants to have a chance, so she's still going to have the Rupert-booting to contend with. It just makes no sense to me for her to risk the rock at this point, and I don't think it's even a very close decision. Finally, she votes.