Complex sentence: Believing she is a full vampire, she is a leader of a Night World group that hunts humans at the beginning of the book but later realises that she is half-human as her mother was a human while her father was a vampire.
Split into simpler sentences: Believing she is a full vampire, she is a leader of a Night World group that hunts humans at the beginning of the book. She later realises that she is half-human: her mother was a human and her father was a vampire.