After they see their 100th comet, Rosalina looks back at her home planet, which then causes her to feel greatly upset and homesick, and then comes to terms with the fact that her own mother is dead.
Rosalina later appeared to Mario/Luigi after Peach is kidnapped.
In order to aid Mario/Luigi she gives him Luma, the same one seen with Peach at the Star Festival.
Once Mario/Luigi collects the first Grand Star, she explains to him that Bowser stole the Power Stars and requests that he help get them back.
Rosalina is a recurring character that debuted in Super Mario Galaxy, first appearing in the Gateway Galaxy.
She is a very powerful figure, as her duty is to watch over and protect the cosmos, while also serving as the adopted mother of the Lumas, and commanding the Comet Observatory.
Rosalina's back-story is chronicled in her storybook told by her in the Comet Observatory's Library in Super Mario Galaxy.Nine chapters are unlocked throughout the game, and the last is unlocked by completing the game.Rosalina's story begins when she meets a young Luma in a rusted spaceship, where they rebuild spaceship to go search for the Luma's mother.They traverse through the space, encountering comets, asteroids, and Star Bits.Rosalina then starts to miss her mother, but the two begin to build a new home that would eventually become the Comet Observatory.As she and the Luma build the home, Rosalina takes more Lumas under her wing.