It is explained in the book and may be more of a plot point in the second season. A vampire must drink the person's blood and then feed them on their own blood for a period of time. Marcus is seen to cut his own wrist and tries to get his dying friend to drink, but his blood is't strong enough to activate the feeding instinct.

Both the ring and the pendant she wears are Teresa Palmer's and not the character's. She does receive some significant items of jewelry in book 2 and presumably season 2.