Until the end of the movie, she only speaks when someone pulls her string. She is one of Jerry's allies on a quest to the star to find the toymaker after Le Petite Ballerina was abducted by the cats who took over the kingdom; however, when they alley-cats lead by Tom soon catch up to her, and a cruel and cold-hearted cat named Dr. Malevolent abused her and forced her to talk by pulling her string, she revealed to them that her friends were on their way to find the star and the toymaker. Distraught, she then felt guilty about betraying her friends and felt like they never wanted to see her again.
During the battle against the cat army, Nelly returns to free Tuffy and Jerry who are eaten by Tom and smashes his teeth with a hammer. She is also shown sacrificing herself for Le Petite Ballerina and Jerry and crushed by a demolished structure, and is resurrected by Christmas magic, and can speak without a string permanently.