My daughter has gone through this.
In a slightly different context, 5rings wrote: "he who treats the site of pain is lost".
Under that philosophy or similar, I did not approve of a doc treating the consequences of what was happening before we attacked the likely causes.
My suspicion was exactly what GM posted, the over-weighted backpack. Add to that study habits that include lying sideways and contorted on a bed or on the floor leaning unsupported against something - for hours. Not exactly on ergonomic design. Never using the chair and drafting table I measured, built, adjusted to fit her.
A lot of it goes back to the textbook racket. There is no reason these kids couldn't be just carrying the pages or chapter they need for each class or just access it all online, instead of carrying 6-8 full textbooks everyday, every where they go. Second idea would be something with wheels pulled like a flight attendant's carry on bag. There was no way she was going to be first to change book carrying habits.
As an aside, same was true with hockey gear. People think hockey is dangerous but I like to joke that 80% of the injuries really come just from lugging the gear in and out of the arena. Athletes too proud to use wheels. A couple of years ago I started noticing all the new expensive hockey bags have wheels.