Kristen Stewart missed Taylor Lautner's Abduction première, just like her beau, Robert Pattinson. RPattz didn't attend the US première, although he didn't have as good of a reason as KStew... she was busy working on Snow White and the Huntsman and couldn't get away. No one really knows why Rob didn't go—it's assumed that he didn't want to steal the spotlight from his friend.
According to Hollywood Life, Kristen Stewart is filming in Pembrokeshire Wales, UK. She has been filming long hours and just couldn't get away to attend the première. The truth is that she may not have even wanted to go (she isn't a fan of crowds or attention), and maybe she also didn't want the spotlight on her.
Although Taylor, Kristen, and Robert are all friends, they give each other space and try not to overstep their boundaries. It doesn't mean that they don't support each other—it's just the type of relationship that they have. And that works for them.