She's at an age when grades start to matter. That means that the stuff that needs to get done - assignments, worksheets, vocabulary words, notebooks - have to be at school when she needs them at school, and at home when she needs them at home. Frequently, they are not.
"A place for everything, and everything in its place" does not come naturally to her. We can coach her, incent her, and give her tools. We can remind her that staying on top of things is her responsibility. But as organization doesn't come naturally to her, she will have to develop the muscle memory to compensate, a defensive reaction to double check that she isn't forgetting something. As it is, she feels the disappointment borne of sloppiness, but she hasn't really experienced a major set back yet as a result. Until she does, it's likely to persist.
As a parent, own goals scored as a result of poor organization are not just irritating, they're disappointing. Of course, disappointing though they may be, they're also proof positive that the acorn doesn't fall far from the tree.