The Fairy Rebel — Lynne Reid Banks

Everyone knows grown-ups never get to see fairies -- they don't even believe in them. But one day Jan, a grown-up, was sitting in her garden feeling sad when she suddenly discovered that fairies can be very real -- and quite extraordinary ....

Tiki knew she'd be taking a terrible chance if she defied the Fairy Queen and used her power to help a human, but Jan was crying because she wanted so much to have a baby. Tiki, who was the kind of fairy who didn't always obey her queen, just had to do something....

Soon, Jan's dream comes true, and she and her husband have a wonderful little baby girl. But Tiki has angered the queen and now she and her human friends are up against the dark and chilling fury of a leader who will not hesitate to unleash her most terrifying powers against them.