Rosie and the other 382 engines of her class were made in Iowa and Pennsylvania in 1942 and shipped to Britain in 1942. After the D-Day landings the engines were sent to mainland Europe to assist with the war effort. Sometime after 1945, Rosie made her way to Sodor.
Rosie began idolising Thomas to the point of hero-worship and imitation. Though this is said to be the most sincere form of flattery, it only served to irritate Thomas whilst he was trying to deliver a special birthday post train to Alice at Hill Farm. After Thomas had an accident in the course of delivering this train, she helped him and he started to respect her.
Rosie later helped Thomas shunt trucks until Hector frightened her away.
Rosie was later charged with acting as back-engine to Emily with the funfair special. Wanting to take the train herself, and thinking she was doing Emily a favour, Rosie succeeded only in creating confusion and delay on a grand scale, but eventually set things right.
Rosie then rescued Thomas when his fire went out after playing a game of "splish, splash, splosh". And she later let Diesel take her train of flowers which were headed for market.