Changeling's Choice: Book II of the Troutespond Series

Alana the Teenage Witch is trying to lead a normal life… fixing doors to the fairy world, fighting the monsters that emerge through them, handing in her A-Level coursework, casting spells, and trapping pixies. Her new best friends have their own problems too, with a doppelganger changeling in their midst.
Another job is waiting for Alana, though. It's all in a day's work for the Piper's protege.
The Troutespond Series is a YA fantasy, working on the premise that if the supernatural did exist, inquisitive teenagers would be the first to notice, and absolutely the worst people ever to interact with it.