Isis appears only once in the series, during the episode, "All's Fahrenheit in Love and War". She is the owner of the Vanderchill Ice Factory. Isis has the peculiarity of always being cold, due to a failed experiment to freeze her face in an attempt to preserve her beauty. She ended up freezing her blood instead, which she feels forced her to "hide her beauty" from the world. She is shown to have an ice beam power, allowing her to freeze surfaces and craft icicles that she uses as projectiles, as well as "Blizzard Breath", which allows her to blow gusts of frigid air at enemies in an effort to freeze them.
Her lair consists of a series of underground caverns filled with hot springs, the entrance to which is initially boarded up in the sewers of St. Canard. Darkwing and Launchpad discover this when they are outrunning a giant snowball, unleashed upon them by Isis's firefly minions; Launchpad notes that the caverns are not on the map.
Upon meeting Darkwing, she immediately develops a crush on him. She flirts with him continuously throughout the episode- much to his chagrin, as expressed by the line, "Why do the weird ones always fall for me?". She offers to help him find the fireflies, only to drag him off on a date, insisting that first, they had to "get to know one another".
While Isis drags Darkwing to various romantic locations (including a restaurant, the movies and an "intimate, little boiler-room"), Launchpad discovers pots of frozen melted gold in the freezers of the Vanderchill Ice Factory. It is later revealed that she intends to coat the entire city in gold, reflecting enough heat to finally keep her warm. She realizes the consequences of her actions, stating that the city will become "unlivable for anyone else", but is unremorseful about their plight. Although she manages to capture both Darkwing and Launchpad, freezing them into one giant ice cube, they manage to escape and gain access to her snow blower, turning it on her, and transforming her into a giant snow-duck. She has never returned since.