In the Books
When the whales pulling the ship start acting strange, Nisha jumps down to check them out. A Wyrm parasite gets into her skin, causing the crew to panic, especially Arac.
Later when Rollan and Abeke fend off the infected Stetriolan people, Nisha and Arac attack them. They both fall over the edge of the ship and don't get back up, which implies that they died or were knocked unconscious.