Sisters of Sorrow by Axel Blackwell

Anna Dufresne lives in a factory that eats children. If the brutal machines don't kill Anna, her guardians' neglect and abuse probably will. The only thing this abandoned teen wants is out. But the factory is inside a stone fortress, on an island, where people are sent to be forgotten. It serves as a dumping ground -- both for orphans who are not welcome at finer institutions, and for nuns who have disgraced the Church. The walls of Saint Frances du Chantal's Orphan Asylum hum with secrets and buried scandal.
In the catacombs below the factory, something long dead, something almost forgotten, stirs. It offers Anna a key, and promises freedom, if she will seek it out when she escapes. She knows her plan will endanger the other children, but Anna cannot resist the call of freedom.
Her escape attempt triggers a chain reaction of chaos, shaking the orphanage to its foundation and laying bare its deadly secrets. As Anna flees into the night, she discovers that the evil nuns were the least of her worries. The swirling mist of the island hides terrors more dangerous than she could ever imagine.