I would love backpack recommendations for my middle schooler. She is required to haul around about 13 lbs of binders and accordion file folders, packed lunch, gym clothes and shoes, and typically has a couple library books as well. I'm worried about the weight of all this on a 5’ tall 75lbs child. Backpacks with wheels are out since she has lots of stairs to climb throughout the day. She walks to and from school, about half-a-mile.