Wait, There Was a Fifth Marauder?

"Wait…there was a fifth marauder?" "And it was a girl?" "And she was in SLYTHERIN?" There was indeed a secret girly marauder with a dark past, a great talent, and a sexy strut. She helped shape the lives of our favorite characters, making a few friends and enemies along the way. Sirius x OC. James x Lily. And lots of marauder fun! Could be considered AU just because of the OC.