Silver and Stone by Felicity Banks

Getting into prison is easy. Getting out is hard. Getting away is nearly impossible. Getting the power to control your own destiny might cost everything you have. Emmeline, Matilda, and Patrick are sworn to rescue Patricks mother from the infamous Female Factory prison, but when a vengeful police officer tracks down their hideout, things get worse fast. Soon theyre framed for a double murder and fighting a magical monster in the eerie and unfamiliar island of Tasmania. Patricks mother hides crucial papers in a tin under her prison smock, and her best friend Fei Fei is dying in the overcrowded prison. More than one womans life hangs in the balance.