S1·E47 Brewster's Little Helper

Zephie admires the 'big' chuggers, and wants to pull freight just like them. Brewster is dismissive when she offers to help him - you have to be big and strong to do the things he does. When Zephie overhears Brewster being given his jobs for the day, she decides to do some of them for him. Then he'll see just how good she is at pulling freight!