Monica first appeared before Ash and his friends while she was in the process of catching a Cleffa that escaped Mr. Backlot's mansion. Afterwards, she took them back to the mansion to get out of a storm and meet Mr. Backlot. They also met all of the Pokémon that Monica cared for. She makes Poffins for them to eat.
Monica takes care of three Pichu in Mr. Backlot's mansion. Pichu and the other Pokémon owned by Mr. Backlot seem to consider Brock's Croagunk an odd Pokémon.