In 1996, she along with her brother Charles Nicholas Hatt helped find and restore Peter, a Stanier 8F, who had been concealed on Sodor. In 2009, after a series of events, she became the North West Railway's controller.
In 1984 at the age of seven, Emily said to her grandfather, Sir Charles Topham Hatt, about Eric and his bravery in defeating the snowdrift near Kirk Ronan. Although mentioned in Cold Wheels, she had a speaking role but was not seen during the episode, Snowed In. Ten years later at the ages of sixteen and seventeen, she was riding her bicycle with a friend when Emily was struck by a green car which failed to stop and fled the scene on purpose. Toby took Emily to see Bridget Hatt at the next station and the girl was taken to hospital for an injury to her right leg. After the accident which Emily's bike hit some boxes and fell into pieces, Percy managed to catch the bad driver behind the incident.
Emily also spoke to Richard Topham Hatt about working in computers rather than being the next Fat Controller on the NWR. She made a cameo in Darkest Hour at Knapford station and returned with Richard Topham Hatt at Knapford Sheds for the Christmas party in Desperate Times. This happened in 1994.
During the summer holidays of 1995 and 1996, she trained as a guard on the Ffarquhar Branch of the North-West Railway, and passed all examinations required to officially qualify as such. Obtaining these qualifications was her idea, to "get an understanding of the family business".
After studying Public Relations at Oxford, she started working in the North-West Railway's 'Department of Consumer & Public Relations' in 1999. By 2005, she had worked her way up to the position of director of that department.
Following Sir Stephen's unexpected retirement in 2009, Norman Spencer was made acting controller of the North West Railway until Friday of that week. Emily stood up for the railway's existing engines, even going so far as resigning to make her point. She was later appointed controller of the North West Railway.
Emily became The Fat Controller after Mr. Spencer resigned from his job following a week of madness which wasn't handled properly by him. Her first year as Fat Controller, 2009, was rather eventful. She handled many situations during this time such as sending Bill and Ben to The Container Yard for temporary work, dealing with a locomotive Thomas knew from his past, setting up the charity special for Tornado and the return of Gordon from his repairs. Other events include comforting both Ben and Thomas, welcoming Lily back on the NWR following the mystery surrounding her and introducing Iris to the China clay twins. Her final event for 2009 was dealing with Patrick's accident outside The Container Yard a few days before Christmas.
In 2011, Emily was rather active. During this year, Emily rearranged the Wild Nor' Wester's schedule after complaints from the other railway. After it was revealed that Gordon was incapable of keeping up with this new change, Emily bought Pip and Emma for the NWR, with Gordon's support. She was also the maid of honour at her friend: Kate's wedding. She, along with Mike, helped to solve a confusion related with the wedding's food delivery; and gave her thanks to the small engines the next day. In addition, she also arranged for a reassignment of the post train; with a single post van on each branch line on the North West Railway as well as four for the Main Line; and for Evan and Edwin to have new couplings and buffers.
- Season 4 - Cold Wheels (mentioned) and Snowed In (not seen)
- Season 5 - A Stranger in Need, Expectations, Darkest Hour (cameo) and Desperate Times (cameo)
- Season 1 STMY - A Change of Scene, Tornado (episode), Ode to George Carlin (mentioned), The Missing Engine, Fame & Misfortune (mentioned), Doncaster Drawn, Separation Anxiety, Last Laugh, Aftermath, Homecoming, Genesis of a Grudge and Taking Care of Christmas
- Season 2 STMY - Swan Song, Surf Line (mentioned), Food for Thought, Percy's Post, Engines of All Trades (does not speak), The Thin Clergyman, Last Straw (mentioned), Dime For Trouble, Caden, Troublesome Trucks (mentioned, not named) and Endgame.
- Sometimes, Emily wears a shirt that says "Shining Time Station" on it. She has also been spotted in a red T-shirt with the logo of the Star Tugs marine on it. And she once wore a shirt with Applejack from "My Little Pony: Friendship is Magic" on it.
- This character is not meant to be confused with Emily from the Thomas & Friends television series.
- She has a tattoo of a violet on her left upper arm.
- She is the first ever female to become The Fat Controller.