Well - something I love to do with kids in the tween age group is find something they LOVE to do, and shoot them doing it! Maybe its a sport, or playing a game... maybe its texting on a cell phone... or maybe its just riding horses, playing with a pet.... anything they love doing is something a mom and dad will want to remember in photos. 
Then I do the usual formal / semi casual poses (eg: on a fence, on a rock.... etc).
A fun one to think about if you're studio shooting, and she is into ipads, computers, cell phones etc.... have it turned on, and make it a big light source. 
Hope that helps, and good luck!