Is she using a locker? So many of the students at our school refuse to use them, preferring instead to carry every item for every class all day long. It's not a good choice.
My daughter uses those super-cheap, flexible-cover notebooks (the ones that go on almost-free sales in August) because they're so much thinner and lighter. They're plenty for one class, and they last for the semester. She likes to keep the notes and notebooks intact after the class is over, so they're never re-used, but when they're almost free, that's fine.
Finally, it's not just LL Bean backpacks that have a lifetime guarantee replacement: It's pretty much all the major names. Jansport, North Face, etc. I used to work at a camping store, and one of my jobs was sending the packs back to the companies -- it wasn't something we had to do often because the vast, vast majority of people just throw them away and get a new pack. But all the big names make the same lifetime guarantee on their seams and zippers (which are the only parts that'd break under normal wear).