We read translations of old Yokudan texts at my academy. I think the lady in the cistern is a depiction of Hazadyya Sea-Queen. She was well-known and respected among her people's descendants, and Prince Hew may have read her Lost Islands of Old Yokuda. Also, the creature wrapped around her is a sea serpent. This means the "queen of the sea" watches over the water supply for the only free port of Hew's Bane, as though it were a colony of Old Yokuda itself. Pompous symbolism - wortly of Prince Hew himself.