A lot of kids start losing interest in school about that age. It comes, usually, from one of two things - school is getting too difficult and the class is getting ahead of her; or school is getting too easy and she's bored.
Take a look at her grades before she started losing interest. If they weren't very good, maybe get a tutor or try helping her with some of the stuff yourself - even the stuff that's not "homework," but any/all of it.
If her grades were really good before she started losing interest, she could be getting bored. Find out from her teacher what they're learning and maybe try to find some extra books or activities along the same lines that may resnag her interest. If this is the case, this is the critical age to regain her interest in school.
I wouldn't jump to conclusions about ADD right away, it could be something as simple as one of these two situations. If you think about it, a typical class has between 20-30 students in it, the teacher HAS to stay with the class average, they CAN'T work with every child at his or her own level. Therefore, those who are struggling a little, get left in the dust. Those who excel, get bored. That's why I homeschool; it's definitely the best solution. However, a lot of people are unable to do it, so I would suggest these other things.
If it does turn out to be ADD, though, try to stay away from putting her on drugs. Theya re SOOOOO bad for the child! You are actually lowering her IQ and definitely eliminating a lot of creativity. The best way is just to spend extra time with them such as suggested above, anyways. Even though, I know you don't seem to have much time for anything.