She is one of five Trainers who can join with the main character during an event in Pokémon Diamond, Pearl, and Platinum. Later, she can join the player in competition at Sinnoh's Battle Tower. She first appears in Eterna Forest. She asks the player to join her because she's afraid she might run into Team Galactic. Her Chansey is good at using restoration techniques like Refresh and Softboiled, but isn't good at offense.
Mothim was first seen as a wild Burmy in the Eterna Forest. Cheryl has spread some Honey on a tree in hopes of attracting a Burmy. After confirming Burmy's gender to be male, she proceeded to capture it. She explained to Ash and his friends that she needed a male Burmy to evolve into a Mothim in order to find the Amber Castle. Cheryl then trained Burmy in order to evolve and it finally did during a battle with Team Rocket.
Mothim was then key to locating Combee and the Amber Castle. Cheryl also used Mothim to help defend the Amber Castle from Team Rocket.
Chansey was the first Pokémon that Cheryl was seen with. Chansey was used in order to determine the gender a Burmy when they came near a honey tree. When Cheryl finally found a male Burmy, she used Chansey to battle it. Chansey weakened Burmy, allowing Cheryl to capture it.
In Diamond and Pearl Cheryl is the only double battle partner the player must team up with to advance through the game. She is also the set default. This means that if ever a player uses a walk-through-walls cheat to go through the places where the other stat Trainers should be for the first time, Cheryl will be there as the partner.
However, this was changed in Platinum, so Riley must be encountered to collect an HM on Iron Island.
