Jennifer's Body (2009)

Nerdy reserved bookworm Needy, and arrogant, conceited cheerleader Jennifer are best friends, though they share little in common. They share even less in common when Jennifer mysteriously gains an appetite for human blood after a disastrous fire at a local bar. As Needy's male classmates are steadily killed off in gruesome attacks, the young girl must uncover the truth behind her friend's transformation and find a way to stop the bloodthirsty rampage before it reaches her own boyfriend Chip.