My Name is not Midnight

Esmerelda Midnight.
Not her true name, but the one she must bear. She is 12, shy, overweight, ungainly. Her destiny is to be a servant to the wealthy Snows and Midwinters, the chief worshippers of Our Lady of the Snows, whose sacred mountain overlooks the bay.
Her teacher, the cruel Sestren Agrippa, is her bane, and also the mistress of the orphanage where Esme lives--the crumbling, mouldering manor where Bloody Bones lives in the cellar, eating bad kids. It seems life will never get better...
Then Esme meets an old man, Reynard the Fox. Mr Reynard turns out to be a wizard, one of the very last. When the land of Adanica fell to ice and fire, his daughter Rosamunda was lost--the last wizard's child with vast powers untapped. He is bound to his mansion of Hall i' the Wood, watched by evil beings...but he begs Esme to find his missing child for him.
The Rose's powers are needed swiftly...for the Sestren are planning for the Great Feast where all humankind will perish. On Hallowmas Night, full of fear and oppression, Esmerelda must get a new Rose to refresh the old Rose's failing powers...but she must climb the Tree of Life on the Island of the Dead.
Then the great Whale-King Skan-ar must bear her across the waves to halt a terrible Sacrifice...