Rosemary and Rue by Seanan McGuire first in the October Daye series is currently $1.99 in the US
https://www.amazon.com/Rosemary-Rue-...dp/B002N83HAW/
https://www.kobo.com/us/en/ebook/rosemary-and-rue-6
The world of Faerie never disappeared; it merely went into hiding, continuing to exist parallel to our own. Secrecy is the key to Faerie's survival—but no secret can be kept forever, and when the fae and mortal worlds collide, changelings are born.
Outsiders from birth, these half-human, half-fae children spend their lives fighting for the respect of their immortal relations. Or, in the case of October "Toby" Daye, rejecting it completely. After getting burned by both sides of her heritage, Toby has denied the fae world, retreating into a “normal” life. Unfortunately for her, Faerie has other ideas...
The murder of Countess Evening Winterrose, one of the secret regents of the San Francisco Bay Area, pulls Toby back into the fae world. Unable to resist Evening’s dying curse, Toby must resume her former position as knight errant to the Duke of Shadowed Hills and begin renewing old alliances that may prove her only hope of solving the mystery...before the curse catches up with her.