Vampire Academy Series Books 1 - 6 Collection Set by Richelle Mead:

Vampire Academy:
Rose Hathaway is a Dhampir, a bodyguard for her best friend Lissa, a Moroi Vampire Princess. They've been on the run, but now they're being dragged back to St Vladimir's where the girls must survive a world of forbidden romances, a ruthless social scene and terrifying night time rituals.

Frostbite:
It's winter break at St Vladimir's, and a massive Strigoi vampire attack has put the school on high alert. This year's trip away from the academy to the wintery peaks of Idaho has suddenly become mandatory.

Shadow Kiss:
It's springtime at St. Vladimir's Academy and Rose is close to graduation, but since making her first Strigoi kills, things haven't felt quite right. She's having dark thoughts, behaving erratically, and worst of all . . . might be seeing ghosts.

Blood Promise:
The recent Strigoi attack at St. Vladimir's Academy was the deadliest ever in the school's history, claiming the lives of many. Even worse, the Strigoi took some of their victims with them - including Dimitri.

Spirit Bound:
Dimitri gave Rose the ultimate choice. And she made the wrong one...After a long and heartbreaking journey to Dimitri's birthplace in Siberia, Rose Hathaway has finally returned to St. Vladimir's Academy - and to her best friend, Lissa.

Last Sacrifice:
The final heart wrenching episode at St Vladimir's Academy.Rose is on trial for high treason and the death of Queen Tatiana. Someone is trying to frame her and it looks like even Dimitri might not be able to save her now.