Anya is a young adult who is tired of being treated like a kid. When she's surrounded by beings who are immortal, she is used to them thinking she is young and naive. She should ideally sound like someone who is confident in herself and her abilities. She has had a lot of pressure placed on her since she was a child. She is able to be serious as well as joking/playful. Her voice is probably higher-pitched to show her youth, but not too high-pitched because she is an adult.