Invincible by Dawn Metcalf - USED

Love must be stronger than fear, stronger than fate.

Invincible.

The future of two worlds depends on it.

Joy Malone has learned to live between two realities, surviving mortal threats and agonizing betrayals. And she's found true love. But the world of the Twixt is in chaos, and the Council wants someone to blame... Facing a danger greater than any she's ever known, Joy must find the strength to rely on herself as her allies fall away, because Joy is no longer sure just who--or what--she is. She knows only that her deepest secret is also her greatest vulnerability and the key to saving them all.

As she fights to protect her friends and family and to unite two disparate worlds, Joy has to trust that some bonds are stronger than magic.