Who is Tori in the novel, Allegiant?

Tori is one of the first characters that Tris meets. They first meet in Divergent (book one) during the sorting ceremony. When Tris's test scores are inconclusive because of her divergence, Tori hides it and saves Tris's life. Later on, after Tris has joined Dauntless she befriends Tori and shows her some of the customs and ways of the Dauntless faction. She sports a hawk tattoo. Later, she is killed as they try to leave the city. This is particularly horrible due to the fact that if Tori had lived one more day she would have been reunited with her brother, whom she'd thought dead all these years.