"What's my name?" "Daddy."

What if Elena had a twin sister Karin who acted similar to Katherine but is a vampire hunter? What happens when they meet the Salvatore brothers for the first time and fall in love without knowing about Katherine and vampires? What if Damon only wanted Karin because she's exactly like Katherin? Will they fall in love for real or just for fun? Her name is Karin Gilbert the other doppleganger.