Has she always had issues focusing, or is this new? I know she was doing fine at her old school, but how about at home? Was she able to read a challenging book, or do a complicated puzzle, or did she wander off in the middle? My youngest is currently being assessed for ADHD, and the doctor said that often times, girls who have the inattentive type of ADHD (without hyperactivity) aren't diagnosed until middle school because that's when the schoolwork becomes so much more complicated. The kids can no longer compensate, and their inability to focus becomes a problem. The doctor was saying that typically, kids like this are unable to focus in class (though perhaps they can focus on things that are intensely interesting to them), they will almost never choose to do things like read a long book, they have trouble finishing tasks and will often wander off halfway through, and they often appear to be "off in their own world." However, they're almost always very intelligent.
Aside from that, having a vision and hearing test seems like a good idea.