Wow, sounds like my oldest girl...I haven't read your other responses, however, have you had her checked for ADD or ADHD? Organizing issues are a major symptom of ADD. We worked with my daughter's teachers throughout elementary school & tried many different things--including separate folders &/or 3 ring binders for each subject. That seemed to make her feel too confused & overwhelmed, BTW. She would cry about how she just couldn't keep things straight & would feel really bad because she knew she had done the work, but she couldn't find it or remember to bring in on time. Yes, many days I brought to school the homework that she had left somewhere around our house. My sister is a teacher & knows the AVID method & set her up with that system, she just couldn't maintain it. We did finally chose to try meds (in middle school) & it has helped her organization (among other things) tremendously. Now she gets 95% of her assignments in to the teachers early. The papers may be rumpled, because the whole folder thing makes her crazy, & she just stuffs the papers in her textbooks, but at least they are turned in. Her backpack is a black hole (still), but she can maintain her focus long enough to do the work & get it into the teachers on time & frequently she is now EARLY with her assignments.
My middle daugther LOVES the color coded folders, labels, matching gel pens & 3 ring binders. She watched her Auntie set up the system for her sister & then she asked me for all the stuff & set up her own, with no help from me or her Auntie. She's been using it since she was in 2nd grade (way before she even needed it), & she never has issues with missing or incomplete assignments. She CLEARLY got the organization gene for our family!
A professional organizer is a great idea, however any system set up has to be simple enough for your daughter to maintain without any prompting from you, so that she can do ____@____.com Luck