Have you tried color-coding by class? You could help her type up an index page for which color goes with which class, ordering the list by her class schedule. The index page could specify taking what is needed for the number of classes she has between locker visits. Scheduled locker visits could also be placed on the list. For each class, the items needed could be listed and/or drawn in quick cartoon style. (For example: Math Book + Blue Ring Binder + Blue Homework Folder. Instrument + Red Ring Binder. Locker visit. English book + Yellow Ring Binder. Spanish book + Green Ring Binder.) Place the index page in a page protector and tape it inside her locker door as a reminder.
If she finds a ring binder to be awkward or time consuming, you might help her find zippered envelopes in different colors. There are mesh ones (9"x11") and there are vinyl plastic ones which are made to clip into a ring binder. All of her "loose" papers could get stuffed and quickly zipped for safe-keeping, to be reviewed and organized later at school (on her own or with teacher/counselor assistance) or at home possibly with parental assistance, coaching, and encouragement/praise.
Whatever method she chooses to try (and she may want to adopt several, adjusting what works and dropping what doesn't)... she needs to buy into it, own it, and be the boss of it... truly feeling like it is her decision of how to best help herself.
