Dragons' Teeth. Red Dragon, #2

Robin spent last summer helping to save the world, after finding out that magic is more than just being able to notice things that most people don't see, and that all sorts of dangerous magical beings are real. Dragons, vampires, elves - and they all seem to think of humans as somewhere between cockroaches and cattle. But her cousin is still missing, although not in the dubious care of the vampires who kidnapped her - and on the way to try to find her before she self-rescuing-princesses herself into more trouble than she can get out of, Robin gets a little bit lost.
In the Otherworld. With the dangerous magical beings who may or may not think she's a cockroach - or maybe, that she's one of them.