YA Fantasy - Girl is a Fairy/ Fae but does not know it. Runs away to the fantasy world

[Nick]

I remember that the girl is a fairy or fea creature but she doesn't know it. When younger she had imaginary friends who where Fairies that she left milk out for. She does this again is surprised to find out they where real.

She ends of finding out she is a fea and that the Fairies have been watching over her.

I remember she goes to one of her friends to talk to him. He offers her a drink and she can taste the backwash and the chemicals since she is becoming for fea

The fairies where going to use her in a plot that would get her killed. A human invading the magic world executed by the king I believe. But the iron shackles burns agains her skin and she screams in agony in front of the fantasy creatures. I am not sure if she escapes or is let go, but she runs off and finds herself in the fantasy world trying to survive and stay hidden as well.

I remember the cover looked hand drawn and had all kinds a crazy cartoony looking fantasy creatures on it.

I read this book in the early 2000s - would have been no later then 2007

Thank you for your time

[Frog]

Holly Black?