Looking for the title of a book for young kids (8-13). The premise of the books is: a "supreme" race that generates planets and is in charge of organizing the cosmos. The leader has several offsprings of which one is put to do deliveries. One day his best friends' parents are annihilated while on Earth (in disguise) but they manage to send a human girl to safety. Throughout the story she has to be put in a bucket because she cannot hold human form for a long time. In the end the "boy" helps her get back at a newly reconstituted Earth, and saves his friend's parents. The book was fairly new in 2014/2015... for the life of me I cannot remember the name or author. Can anyone help?