From the Super Mario Wiki
Mercedes Rose (born March 22, 1972) was the original voice actress for Rosalina. She voiced her in Super Mario Galaxy, Mario Kart Wii and Super Mario Galaxy 2 before being replaced by Kerri Kane. Rose has a family-run business in the film and television industry and describes herself as a Creative Entrepreneur.
Mercedes Rose was born in the United States of America, in Salem, Oregon, Oregon. She eventually took up acting, and does work in commercials and advertising. Her introduction to voice-acting came in 2001 when her agent called her down to an audition without telling her it was a voiceover role until she arrived. Always working on expanding her skills, Mercedes went along with it and has been doing professional voiceovers ever since. While she still does live-action spots, she favors voice-work, and has even created a school dedicated to sharing the skills of a voiceover career, Voiceover Driving School. Mercedes Rose also has her own in-home studio which includes state-of-the-art equipment and software.
Prior to getting the role of Rosalina, Rose had never seen a Mario game, only having played Pac-Man and Space Invaders. For her audition for the role of Rosalina, Rose used her "natural mom voice," as Rosalina was described as the mother of the Lumas. Rose states one of the things that attracted her the most to the role was the fact that Rosalina was the first Mario princess in many years. In a 2016 interview, she made it clear it was not her decision to stop voicing Rosalina, though having worked for Nintendo gave her many other professional opportunities.