Sanguine by Carolyn Denman

Lainie Gracewood has turned her back on the world she used to call home. But who can blame her? After all, the sweet bliss of paradise is hard to resist.

But there's a restlessness inside her that yearns to be set free. When a native Edenite discovers the boundary between Earth and Eden, Lainie promises herself a return will be short and sweet.

As always, Earth is more complicated than that. When a Guardian is abducted, the urge to protect the sacred knowledge will see her faced with the ultimate choice: life, death or paradise?