Rosalina first appears in Super Mario Galaxy. There, she acts as an ally to Mario. After Bowser attacks the Comet Observatory, she gives Mario the task of getting back the observatory's Power and Grand Stars. She also gives Mario a creature named Luma to help him in his adventure.
In the sequel, Super Mario Galaxy 2, a figure like her named the "Cosmic Guide" appears in the game when Mario dies multiple times in a level. Rosalina herself appears during the credits.
Rosalina makes her first playable appearance in Mario Kart Wii. She is an unlockable character. Rosalina later appears in Mario Kart 7. There, she is again an unlockable character. She also has her own track called Rosalina's Ice World.
Rosalina appears in Super Mario 3D World, where is she an unlockable character. She can use the spin attack move that Mario can use in Super Mario Galaxy.
↑Nintendo. Super Mario Galaxy 2. Nintendo. (2010) “Rosalina: I would like to give you my thanks.”
↑Official Game Bio: "Making her debut on the track, Rosalina shows her experience of space travel translates well to rocketing round the race course. With a friendly Luma by her side, Rosalina is right at home on the track!". Nintendo.