This picture is a poster based on my idea of how Equestria Girls should be.
 
The Mane Six are sent to earth on a mission from Celestia in order to study human culture and ways. They do this by taking the disguise of high school girls. However because Earth has little to no magic they will have to get used to human technology and culture.
 
However should a threat befall Earth or Equestria the girls would transform using the Elements of harmony into anthro pony forms wearing armor; the “Knights of Harmony”, in order to fight off these threats to Equestria and Earth.
 
I even came up with some good human names for the girls to use “In Public”.
 
Twilight Sparkle = Twila Sela  
Rainbow Dash = Rene Dart  
Rarity = Rachel Upson  
Applejack = Jacqueline Applin  
Pinkie Pie = Diana Pierce  
Fluttershy = Sarah Fluster