While it looks like she wants that hug to end as soon as possible, you can rest assured that that's just how Kristen Stewart's face looks all the time, regardless of emotion. For confirmation, watch any of her movies.
Well congratulations, girl. While most people managed to ruin celebrities' days through sheer cringe-worthy awkwardness, you specifically set out to ruin Peter Facinelli's day by arming yourself with the saddest news possible. It seems especially cruel, since you could've accomplished the same thing by just reminding him of his role in The Scorpion King.