"Never. Never. Have I let anyone off this train before they reached their destination. Some have tried - Sirius Black and his cronies, Fred and George Weasley."
-- the Food Trolley Witch (CC1.11)
Scorpius Malfoy follows Albus Potter onto the roof of the Hogwarts Express. To their surprise (and alarm), the Food Trolley Witch appears and tries to keep them on the train. They jump off before she can capture them.
The Trolley Witch tells them a little about her history and role on the train but, frighteningly, she no longer remembers her real name (CC1.11).
The Minister for Magic between 1827 and 1835, Ottaline Gambol started The Hogwarts Express service and installed the Food Trolley Witch onboard (Pm).
From the Web
The theatre production opened in the West End of London at the Palace Theatre on 31 July 2016, with Sam Clemmett in the role of Albus Potter, Anthony Boyle as Scorpius Malfoy and Sandy McDade as the Trolley Witch: Harry Potter and the Cursed Child, Parts One and Two