Shaede Assassin series by Amanda Bonilla

In the shadows of the night, Darian has lived alone for almost a century. Made and abandoned by her former love, Darian is the last of her kind—an immortal Shaede who can slip into darkness as easily as breathing. With no one else to rely on, she has taught herself how to survive, using her unique skills to become a deadly assassin. When Darian's next mark turns out to be Xander Peck, King of the Shaede Nation, her whole worldview is thrown into question. Darian begins to wonder if she's taken on more than her conscience will allow. But a good assassin never leaves a job unfinished...

“She needed a bargaining chip and this was it. Raif’s daughter’s life for hers. And he knew damn good and well I was right. Just like he’d assured me the night I’d killed Azriel, this was far from over. His daughter was alive, I knew it. And I was going to find her.”

For months Darian and her Shaede guardian Raif have searched for the Oracle who attempted to overthrow the Shaede Nation—and kill Darian in the bargain. But now that they’ve finally found the half-crazed Oracle, for their efforts they are granted a possibility too painful for Raif to imagine, and too enticing for Darian to ignore.

Darian is determined to reunite Raif and the daughter he thought was dead, but her mission quickly proves dangerous when her lover Tyler is almost killed. And when a brooding and mysterious Fae warrior offers his guidance—at an extraordinary price—Darian finds herself willing to risk everything. As her single-minded hunt turns into an obsession, and she and Tyler grow further apart, Darian finds herself caught between the man she loves like a brother, and the man whose love she can’t live without…