The Construction of a heroine...
Names have meanings, social stigmas, expectations. A huge part of your personality is your name. You know those people that hate their names and choose another? They don't do it to disrespect their parents, but because their name doesn't fit them. When you hear the name Vivian it portrays a vivacious woman. Can you picture Vivien Leigh in Gone With The Wind? True, not everyone fits the expectation, but it's that instant impression of a name that is so important when there is no physical person standing before you, only a description from a book floating around in your head. The heroine of In the Dark? She has no choice but to trust the hero, and because of their unique situation, he must also put a great deal of trust in her. Blind trust is having faith. The true heroine of In the Dark? Faith.
Faith is Everything
Faith is not simply the heroine, she's the reader's window into this fantastic vampire city. If not for her human perspective, you might not easily acclimate to a society of vampires.