Last Sacrifice by Richelle Mead

Last Sacrifice is the sixth book in the #1 New York Times bestselling series, Vampire Academy by Richelle Mead.
The novel Last Sacrifice begins with Rose in her prison cell contemplating the charges brought against her and occasionally using the bond to slip into Lissa's mind to view goings-on at Court. During Queen Tatiana’s funeral, statues outside the church suddenly blow up, causing chaos, and acting as a distraction for the guardians. Rose is soon broken out of prison by Mikhail, Eddie, Adrian, Abe, and Dimitri. Dimitri takes Rose out of Court and they drive for hours until they reach Sydney, who is also aiding in the escape. They continue traveling until reaching West Virginia, where Rose discovers she is to be kept in a motel until her friends back at Court can clear her name. However, she insists on leaving and helping out, but after Dimitri halts her escape, Rose convinces him and Sydney to look for Lissa’s half-sibling. For safety, Sydney takes them to the Keepers, a strange group of Moroi, Dhampirs, and humans. Later, they find out the sole person who holds the information needed to find Lissa’s sibling: Sonya Karp, who was once teacher at St. Vladimir's but is now a Strigoi. The Dashkov brothers invade Rose’s dreams and they later meet up with her at Sonya's house in Kentucky, where Robert changes her back into a Moroi by staking her with a silver stake infused with spirit. After recovering from the initial shock of being restored, Sonya leads them to Jillian Mastrano’s house in Michigan, who is revealed to be the illegitimate child of Eric Dragomir. (Summary by Wikipedia)