Thalia black was one of the many vampires who lucky lucky got trapped in that tomb for one hundred forty five years. Thalia was bestest friends with Katherine, they were attached to the hip. Thalia is five years older than Katherine but Katherine turned first. Thalia was basically Katherine’s older sister, but not by blood. So when Katherine got stuck in that situation with Niklaus Thalia understood that might be the last time her saw her.