Who is Adelina from The Power of Six and what is their importance?

Adelina is Marina's Cepan. She is forty-two (she looks older) and has auburn hair with grey streaks running though it, which she wears in a tight braid. Over time, Adelina lost her belief in the Legacies and told Marine they were nothing more than fairy tales. When the Mogadorians arrive, Adelina realizes her mistake and battles for Marina's life. In the end, she sacrifices for Marina in the process of killing the Mogadorian who discovered them.