She first appeared telling supposed "fortunes" that when, in truth, what she was telling was obvious, such as when she said a mouse was in great pain because she saw he had a cast on his leg. She despises Nelie Brie for doubting the Night Monster exists.
She later appeared in the sewers meeting her henchmen, a group of cats. The leader of the cats, Twitch, starts taunting her about being shunned by the other dogs because she looked like a rat, but she countered by telling the cats that she was the reason that the cats even had food to eat because she had invented the Night Monster.
She then lured Fievel, Nellie, and Toni to a house with supposed clues about the Night Monster, only to ambush them with the robotic monster. Just as they are about to catch Fievel and Nellie, Toni crushes the robot with a chandelier.
The cats turn on Mousey, as they can get into the mouse's village, but Mousey warns them that the mice will know they are there and lose the element of surprise. The cats kidnap Fievel's father, mother, and baby sister, and have them locked in cages with dozens of other mice. Then Nellie, Fievel's big sister Tanya, and Reed appear and she reveals that she had been compared to a rat for a long time by other dogs, and that she had escaped from her owner and planned to get rid of the mice as revenge. However, Fievel appears from behind and electricutes her, knocking her out. After her henchmen are defeated, she is returned to her owner.