Jennifer is a pink tender engine that works on Thomas' Branch Line.
In Jennifer's debut, she was brought to the North Western Railway to help on Thomas' Branch Line. It was then revealed that she and Thomas used to work together on the London Brighton and South Coast Railway, along with Stepney and Boxhill. She also became friends with Percy, Toby, Madison and Mavis. Rosie, however, did not get along very well with Jennifer .
Later on in the season, Thomas was send to help at Bridlington Goods Yard on the Mainland. Mr. Hatt then made Rosie and Jennifer work together at the Ffarquhar Quarry while Mavis was doing Toby's work, while Toby did Thomas'. After Rosie left the quarry to take a train of stone to Brendam Docks, Jennifer started to work by herself. She then started to sing a song, not knowing that Rosie could hear her. Rosie ran off crying, causing Jennifer to race after her. The two then ran into Mavis, who scolded them. That night, the two of them made up and became firm friends .
Later, Jennifer was decorated for May Day and participated in the Best Dressed Engine competition .
Jennifer is a very kind and excitable engine. At first, she was proud of her pink paint, but now, she doesn't care if she gets it dirty or scratched as long as she's being Really Useful.
Later on in the series, Jennifer is also shown to be excitable, energetic, and a bit of a chatterbox.
Jennifer is based on a London Brighton and South Coast Railway Class K 2-6-0 tender engine. The real engine carrying her number (337) was the first of the class built, being built in September of 1913. Unfortunately, the real No. 337 was scrapped in December of 1962.
Jennifer is painted pink with green lining. She has red siderods. She also has "LBSC" on her tender in red and her number "337" on the sides of her cab in red. She has a brass dome.