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 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.