Isabel worked with Oliver and Toad on a branch line in the West Country. In 1967, the branch line was closed and Oliver's crew plotted an escape to the Island of Sodor. They were nearly caught by diesels several times, and eventually made it to Barrow-in-Furness, where Oliver ran out of coal. Shortly afterwards, Douglas helped the group escape across the bridge to Sodor and stored them at Crovan's Gate; Oliver's crew hid inside Isabel during the journey. Sir Topham Hatt then had the three repaired and repainted in Great Western colours for work on the Arlesburgh Branch Line.
The Fat Controller was already making plans to acquire an auto-coach for the purpose of handling passenger traffic on the re-opened Arlesburgh branch. The coach turned out to be Dulcie, and thus the arrival of Isabel, with Oliver, to augment the stock could not have been better timed. The two were joined by Alice and Mirabel shortly after, who were paired with Duck.
Oliver says Isabel is very clever, as she always keeps a good look out when he pushes his trains and can't see where he's going, and talks to him with her bell. He finds them to be funny coaches, and believes that they would not know what to do without him. Despite what Oliver thinks, they are very faithful to him and are easily able to see when he's headed for trouble
Isabel and Dulcie are based on British Railways Hawksworth auto coaches, which were used in push-pull service on branch lines - while designed by Hawksworth for the GWR, they were never built until after British Railways was formed. The auto coaches were efficient because it eliminated the need for the engine to run around to the other end of the train to turn around. 15 examples of this type are preserved.
Isabel and Dulcie are painted in the Great Western's chocolate-brown and cream coach livery. When the former first came to Sodor, she was painted in the British Railways' maroon coach livery with yellow lining. Dulcie was also seen in this livery in the 1985 annual.
- Enterprising Engines - Escape (Isabel only; does not speak) and Little Western (Isabel; does not speak; Dulcie, mentioned)
- Oliver the Western Engine - Resource and Sagacity and Bulgy (cameo)
- 1976 - Famous Engines
- 1979 - Annual
- 1980 - Annual
- 1987 - The Island of Sodor: Its People, History and Railways (mentioned)
- 2005 - Sodor: Reading Between the Lines (mentioned)
- Isabel's name is a pun on the fact that there "is a bell" on her.
- Isabel's name is misspelled "Isobel" in the ERTL range.
- ERTL (Isabel only; maroon; discontinued)