Who is rosalina in Mario?

Rosalina is the 'princess' of the Comet Observatory in Super Mario Galaxy. She is in the main hub and is the 'Mama' of the Luma's.

Well I know that's right but if you want to know how to unlock her in Mario Kart then first open the mirror cup by racing on all 150cc cups and you HAVE TO GET 1ST PLACE ON ALL RACES!!! Then you should unlock Mirror Cup and Princess Daisy. Race on all mirror cups and get a good ranking most likely star ranking then you should unlock her!!! Hope my Mario Kart advice helped =-)