Small Persons With Wings by Ellen Booraem
Mellie thinks she might be crazy.
In kindergarten she had a fairy friend - I'm sorry, 'Small Person With Wings', (they hate to be called fairies!) - so... she had a 'Small Friend', and she wanted to bring it in for show-and-tell to show the other kids his wings and how he could do magic. She was hoping that it would help her make big friends. But when her 'Small Friend', Fidius, found out her plans to show him off like a pet, he was furious and he disappeared. The next day, her kinder-classmates all thought she was a liar and started calling her names.
By the time she's thirteen, she's a social outcast at school. But then she gets a chance to completely start over. Her grandfather dies, leaving her parents an inn, so the family moves to a new town. When they arrive they find a rundown, mold infested, and generally trashed inn. And on the very first day Mellie also finds... you guessed it - a Fairy! ...sorry! a Small Person With Wings (they hate to be called fairies!) She thinks she must be crazy. "Small persons with wings don't exist!" At least that's what she's been telling herself all these years.
Well, it turns out that her parents know about the Parvi Pennati (that's Latin for small persons with wings). Her father's ancestral line has a thousand year pact with a bunch of Parvi Pennati. In exchange for sanctuary, the Parvi offered his family a Moonstone, which enables the wearer to see the truth so nobody can lie to you. Grandfather was supposed to tell Mellie's dad where he hid the Moonstone for safekeeping, but he didn't. So where's the Moonstone now?
To find out more about the mystery, the magic, and the mayhem, read "Small Persons With Wings (they hate to be called fairies!)" by Ellen Booraem