It's an old wives tale. This woman's flip flops did nothing for her IMHO; you'll note she was still shocked. Lightning has too much power behind it to be bothered by a thin layer of rubber; after all it's already traveled through thousands of feet (sometimes several miles) of insulation (air) before it hits ground.
One out of two lightning bolts starts from here and goes there and vice versa. It’s a polarity thing.