The pilot reported that, during a discovery flight, he allowed the passenger to assume control of the airplane and guided her through various maneuvers. The passenger remained in control until reaching short final of the landing. The pilot noticed that the approach was slow and steep, prompting him to take control. He executed an early round-out maneuver and flare, but realized the airplane was too high and was responding poorly, leading him to initiate a go-around procedure. Right before he could increase the power, the left wing experienced an aerodynamic stall and dropped, resulting in contact with the runway. The airplane sustained substantial damage to the left wing. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.