Rosie is an anthropomorphic female chipmunk with light brown and cream fur, gray hair that she keeps in a bun, and orange eyes. For attire, she wears a light blue dress and a red cape with a hood.
In the past, Rosie lived in Mobotropolis, where she served as the nanny for Sally. She also looked after other children such as Sonic, Rotor, Antoine and Bunnie. In 3224 though, after Dr. Robotnik came into power, Rosie brought her young charges to Knothole Village, where they were safe from the evil doctor. However, she was later caught in the Great Forest by Robotnik's Worker-Bots and roboticized.
Rosie's past was later drastically altered when Sonic and Sally used the Time Stones to go back in time to stop Dr. Robotnik before he rose to power. In the past, Sir Charles called Rosie to a small hut on the outskirts of Mobotropolis after meeting present-day Sonic and Sally. She soon arrived with young Antoine, young Rotor and young Bunnie. Upon arriving, Chuck told her to take care of the children, and if anything unusual happened, she should take them to Knothole. Rosie thus stayed to look after young Sonic, young Sally, young Antoine, young Rotor and young Bunnie, but the children eventually snuck away. Rosie later went to Robotropolis to find the children. There she met present-day Sonic and Sally, who took her with them to save the children. After the heroes saved the children from the Roboticizer, they fled with Rosie to a hut on the outskirts of the city. There, Rosie asked Sonic to remove the furniture blocking the secret passage in the wall that led to Knothole. After Rosie led the children into the passage, she told present-day Sally that she had deduced her identity from the beginning. In response, Sally asked Rosie to never leave Knothole. Though she did not know why, Rosie agreed to it, and joined the children in the tunnel. Keeping Sally's promise, Rosie stayed in Knothole always, meaning she never got roboticized. As such, by the time Sonic and Sally returned to the present, Rosie had prepared dinner for them, and sent Tails to get Sonic and Sally.
Rosie is a kind-hearted and caring woodchuck. According to Charles, she is very prompt, and according to Tails, she is a good cook. Her ability to recognize "Alicia" as Sally indicates she is also quite intelligent and perceptive.
Rosie is good at keeping promises, willing to stay in Knothole undisturbed for about eleven years in order to keep her promise to Sally.
In other media
In the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics, Rosie's full name is Rosie Woodchuck. In this media, Rosie was once the nanny to the royal family and helped raise the young Princess Sally Acorn after the Great War. Rosie was a bit softer-spoken than her cousin, Julayla Chipmunk, but no less wise. With the help of her highly skilled and learned cousin, Rosie was instrumental in getting the next generation evacuated from Mobotropolis to Knothole during Dr. Ivo Robotnik's takeover. With the First Robotnik War came many casualties, and with those casualties came orphans. Rosie tasked herself with providing a loving presence for all the children and helping them grow into their full potential, with the prime example of her skills being exhibited in the Knothole Freedom Fighters. Rosie would later carry on in loving memory of her late cousin.
In the reality created by the Super Genesis Wave, Rosie was the nanny of the royal family, often providing guidance to the young Princess Sally Acorn. When the Eggman Invasion arrived, Rosie was instrumental in helping the next generation evacuate to Knothole Village. There, she acted as the caretaker for the children who would grow up to become the Freedom Fighters.