Foul is Fair (Fair Folk Chronicles)

Lots of girls play Fairy Princess when they're little. Megan O'Reilly had no idea the real thing was like playing chess, guitar, and hockey all at once. Megan had known for a long time that she wasn't an entirely typical girl. But living with ADHD—and her mother's obsessions—was a very different thing from finding out she wasn't entirely human. Somewhere out there, in a completely different world, her father needs help. There's a conflict, revolving around Faerie seasonal rituals, that could have consequences for humanity—and if Megan's getting the terminology straight, it sounds like her family aren't even supposed to be the good guys. As she's further and further swept up in trying to save her father, Megan may be getting too good at not being human.