The Demigod Chronicles: The Lost Items

Seven girls, Casey, Lillianna, Cassandra, Lynn, Dawn, Adrianna, and Valerie, find out that they are demigods, half mortal and half god. All of them have a different godly parent and different backgrounds. The girls all end up together though when they arrive at Camp Half-Blood, a place where demigods are safe. Someone steals a sacred item from each of the twelve Olympians. A prophecy announces that the seven newcomers are to go on a quest to find the items and return them to the gods before complete and utter chaos ensues. The prophecy mentions that one of them is a traitor. Who is it? Is she the thief, or did she help the thief? The prophecy also says that one of them might not return from the quest. Who is it? Does it mean that she will die, or will she just be left behind?

*All rights go to Rick Riordan*