I think we have the same child
I'm assuming this isn't something like ADHD, which I'm not qualified to say anything about, and she's just an...wait for it...adolescent
*Does your school have a website that allows you to keep up with her homework assignments, upcoming tests, and long-term projects? Ours is a godsend. It also covers things like permission slips that have to come back in, standardized testing dates and deadlines, and school lunch money accounts.
*Is she required by the school to buy an agenda, or assignment book. My daughter's book must have each assignment written in it and signed off by the teacher when complete.
*When you meet the teacher(s) at the meet-and-greet (this is usually a couple days before school),or ASAP, ask them if they would mind you calling every Friday to make sure she's caught up and on track. At least if she does get disorganized, it's only a weeks' work and not a semester.
*Some schools have after-school programs that also involve a "study hall" or tutoring, to finish homework.
*I've made a rule that all homework has to be completed and signed off by me before any after-school fooling around. Obviously, if there's sports or band practice, that's an exception.
*I know she has to take "core" classes, but is there a field she's interested in yet? When she reaches high school, she might have more leeway in her classes and might organize herself if she has a goal.
Good luck! It's a challenge. I contrast her with my son, who alphabetizes his folders in his backpack.