It was stated she was in the process of unloading her equipment.
One possibility: She unlocked the PC doors and then carried a load inside to wherever she intended to hold class. Then heading back out to her truck, stopped by bathrooms to turn on lights and make sure they were stocked.
I do remember that quote, but my thought is that is still how I would describe it. If her normal routine was to open the front doors to go unlock the PC doors to unload, I would say she was in the process of unloading. If she had more than one trip of stuff to unload, my guess is she would carry some items with her as she went to unlock the front doors as well.
I just can't seem to come up with a viable scenario where she enters the PC doors, is killed in the SW corner, is seen entering on camera but the killing isn't filmed.