I this book a lot. It was about Philippa whose best friend just moved away. There's a new girl Daisy, but she's really a fairy and she's Philippa's fairy godmother but she made it look like their the same age, so Philippa asked to be called fairy godsister. Daisy didn't like working with the humans because her friend got killed doing one before he ended his life cycle. At the end, Daisy and Philippa were friends.
Title (if read many since last log in, pick one)
Philippa's Fisher's Fairy Godsister