How (Not) To Make Bad Children Good — Emma Barnes

Ever since she bit Father Christmas when she was six months old, it's been downhill all the way for Martha Bones. She is horrible to her baby brother Boris, elder sister, Sally, and her parents are in despair. Far away from Earth, Martha's behaviour comes to the attention of the Interstellar Agency whose aim is to make bad children good. Fred, an Interstellar agent with a poor track record, is sent to Earth as Martha's guardian agent. His mission  to make Martha good, but Martha has other ideas!