Nightshade by Evelyn Lederman
Afton is not like other college freshmen. She drinks blood. Rescued from the horrific Nightshade universe as a baby, the half-ling Afton is manipulated into returning to the world of her birth, where danger shadows her every move. Lorenz never expected to have to fulfill the treaty he entered years ago. He is shocked when he sees Afton for the first time. In his eyes, he only sees the beautiful vision she will transform into, rather than the waif who is terribly malnourished. Forced to live-up to the terms of the agreement, he joins with the half vampire, half human daughter of his adversary. Determined to safeguard his soul mate, Lorenz will do everything in his power to protect her. Will an ancient order dedicated to the purity of vampire blood, succeed in eliminating Afton? Find out what happens when a vampire and a half-ling soul mate come together.