since it's a silhouette, you don't have the information necessary to determine which way she is actually spinning. The way that she bounces up and down further goes to mask it. So your brain has to fill in the body features for itself (ie: 'her left leg is in front of her right leg' or 'her right leg is in front of her left leg')
kinda related is something we did in physics a week or so ago 'a conservative reaction can be taped and played backwards and will look exactly the same' xD