AM Ballroom instruction teaches that the lady takes her first step back on her right foot. For the box basic, the timing and count is the same as in the video (1-a2, 3-a4). The lady takes her first step straight back with her right foot (1-), then takes the left foot to the back-left (a) and then closes the right foot to the left foot (2). So, the footwork happens on the same counts, but the ladys left foot steps back and to the left instead of straight back as in the video.
After that, the lady's left foot steps forward, then the right foot moves forward-right, then the left foot closes to the right. That completes the box and it can then start over again. Hope this isn't confusing :)