Air Born by Rayanne Haines

Quinn Taleisin hates secrets, and shadows, and subterfuge. Which is why she still can’t believe she agreed to become a member of the Guardians, an elite force of immortals tasked with keeping the balance between good and evil in the world.
Sounds great, except, to be a guardian you must agree to live in secrecy. Quinn is a wind elemental. Being caged in by secrecy is worse than death for someone like her. She can’t imagine a worse fate—until she’s asked to work with Lachon Findel, the man she holds responsible for her mother’s death and her father’s insanity.
Lachon is the oldest living elemental in the world. Known as Lachon the Law, he’s an earth element; a man who sees the world in black and white, right and wrong. So maybe once, briefly, a hundred years ago she thought he was a good guy. She knew better now. No way would she fall for his savior of the world shtick.
When the dangers of the past catch up with them, Quinn realizes the only way either of them will make it out alive is if she can put the ghosts of the past behind her and finally trust the flesh and blood man in front of her.