Nak attacked the River Queen on the night Lief, Barda, Jasmine, and Dain were aboard. She played around with Jasmine—who was in disguise as a fancy lady—and tore off her outfit. This caused an Ol who had been hunting the companions to reveal itself, and the pirate's escaped in the confusion.
She and Finn later captured the companions when they arrived at the Maze of the Beast. After tossing them in with Milne (who has betrayed the pirates) she and Finn remained back at the pirate's cave while the rest went to trade Dain to Grey Guards. They witnessed the companion's escape from the Maze and charged at them, swords drawn. However, they moved too close to the blowhole, and it showered them with water, knocking the pirates into the blowhole to their deaths.
Nak's role in the anime is largely the same as the books. However, she and Finn are not killed. Instead, the companions are able to overpower them and leave them tied up to face the wrath of their crewmates for letting prisoners escape.