it was the very night when Luke, Annabeth, you and Thalia was running to camp from some monsters, there were swords clashing against the monsters skin but they wouldn’t give up. Luke, you and Annabeth got away for a little leaving Thalia to make a choice, run or sacrifice herself, being the selfless person she is she decided to sacrifice herself, and that gets Zeus’s attention, so to save not only Thalia, but the whole camp. Zeus turns Thalia into a tree, placing a protective shield on camp