Erika appeared in Pokémon Scent-sation!, running a perfumery in Celadon City where she sold a special brand of perfume made from the essence of her favorite Pokémon, Gloom. Misty, Brock, and Pikachu were enamored with the scents, but Ash insulted the perfume. In protest, the manager, who was later revealed to be the Gym Leader Erika, had him banned from her store and by extension the greenhouse/Celadon Gym.
Jessie and James were sneaking into the gym trying to steal the perfume scents to sell them, but they were stamped with a red X and banned from the gym, too. Ash found them and untied them in exchange for help entering the gym.
Disguised as a girl named Ashley, Ash signed up as a student at the Gym. Erika was reading a fairy tale to some Grass-type Pokémon when he found and recognized her. Pikachu instantly recognized Ash and exposed him. Erika finally agreed to a battle for the Gym Badge. She turned out to be very confident in her abilities, but became too confident when Ash used his Charmander - as Fire was Grass Pokémon's greatest weakness - when she tried to use her Weepinbell. However, their match was interrupted when Team Rocket started a fire in the Gym as revenge for being thrown out.
Ash risked his life to run in and rescue Erika's beloved Gloom, who had once saved her from a wild Grimer when she was a little girl. Out of gratitude, Erika awarded Ash with the Rainbow Badge.