Katie's first attempt to take a step onto the ladder is unsuccessful. As her leg lifts upwards the body rotates backwards with the movement due to the awkward height of the box, her foot has to be placed on the floor again to right the body and box before the foot can be lifted safely.

Her body angle is awkward as she climbs up the ladder, her spine is twisted to allow room for the box and to allow her legs to walk normally up the ladder. As each step is taken  the box is shifted in a circular motion with the rotation of the shoulder to help shift it up the ladder.
When at the top of the ladder it is all about balance and weight shift, initially she can only place the box on the shelf with one hand but as the box gets pushed further back she can lean forwards to a more comfortable position where her body weight is balanced over both feet and she can use both hands.