I’m no animation expert, but based on how she’s moving I believe that this is an example of inverse kinematics, a technology that controls the physical motion of an object according to a mathematically defined internal structure. (Like I said though, not an expert. If you’re an animator and think you can tell what’s going on, do share!)

However they did it, it is impressive as hell. Yes, her bow and quiver clip through the horse, and yes, this isn’t the first game to have someone rearrange their legs while on horseback. All the same, look how she slows her leg down when she’s coming back around to the front. We live in an age of wonders.