Emily is a large green engine.
Season 1 - Paxton Helps Out, The New Diesel Fuel (cameo), Rusty and Victor (cameo), Dave the Diesel (cameo), James and the Ice Cream (cameo), Funny Jokes, and Dash and the Fair
Season 2 - Trevor and the Mud, The Magic Railroad, Sugar, Sodor Blackout (cameo), Hiro goes Home (cameo), and Off to the Scrapyards
Season 3 - Red Paint, Replacing the Logging Locos, The Adventure, and Snowmen
Season 4 - Muddy Thomas, The Return of D199, The Trouble with Trucks and Bulgy's Chickens
She is likely to appear in Season 6