Ambrosia

The second book in the Frost and Nectar series follows a heroine who, after a near-fatal encounter with the Seelie king Torin, passes through a portal into the Unseelie realm known as the Court of Sorrows, where she discovers she bears the horns of its people. Marked as an outsider in both courts and accused of being a traitor by Queen Mab, she must stay close to Torin to survive, despite the enmity between their kinds and a curse that threatens anyone he loves.