Harry Potters Twin Book Three

This year Nixie Potter is determined to beome an anmags. She practices in the shreiking shack with a stray black dog she found when she runs away from the dursleys. She doesn't know who the dog is, or why it follows her, but it does create suspicion from Snape and Dumbledore as to why Nixie disapears everytime Sirius Black esapes into the castle. Will Nixie become an unregistered animagus, will she ever forgive sirius for not showing himself, what will she say to the unexpected news that Remus gives her?