The Vampire Diaries season 3 finale, "The Departed," ended with the revelation that Elena (Nina Dobrev) had been given vampire blood to save her life -- meaning that she was beginning the process of turning into a vampire herself. When season 4 begins, she'll be undergoing the transition, as the recently released season 4 premiere title indicates. According to TVGuide, the first episode of season 4 will be titled "Growing Pains."
Elena's going to be coping with a lot of pain. For instance, there's the fact that Alaric died in the car accident that temporarily killed her. There's also the fact that she finally chose Stefan over Damon, claiming that she if she had met Damon first, things would have been different. And after that flashback revealed that she HAD met Damon first (but he compelled her to forget), it's almost certain that she'll eventually remember, putting her decision to stay with Stefan into doubt. Also, there's the physical and mental transformation into a vampire, which can't exactly be pleasant.
TVGuide also brings up the point that "our Mystic Falls gang is heading into their senior year," with "plenty of 'normal' high school struggles to go through as they reach a big milestone in their lives."
The Vampire Diaries recently nabbed actress Grace Phipps to portray April, "a natural beauty with a bit of an edge" from whom Elena tries to hide the supernatural secrets of Mystic Falls.
The Vampire Diaries season 4 premiere, "Growing Pains," will air on the CW on October 11, 2012 at 8/7c. The show's third season will come to DVD and Blu-ray one month earlier, on September 11.