"I've never been to Hogwarts. Pretty lax security here isn't there?"
-- Delphi (CC2.14)
Meeting on the staircases, Delphi reveals to Scorpius Malfoy that she hasn’t been to Hogwarts before, having been too sickly as a child to attend. She is nervous and careful not to be seen by anyone else. She talks to Scorpius about his friendship with Albus Potter – and how the separation is bad for them both (CC2.14).
The same day as the previous event, September 2020
This event takes place during the Roseless timeline, as described in the essay "Albus Potter and the lesson in Quantum Mechanics" by Nick Moline.
Earlier when she first met Albus, Delphi says:
"Have I just put my foot in it? It’s what they used to say about me at school. Delphini Diggory - there isn’t a hole she couldn’t dig herself into." (CC1.6).
However talking here to Scorpius she says she hasn't been to school. The mysterious Delphi may be telling lies, but neither Scorpius nor Albus is able to put what she says together - yet (CC2.14).
From the Web
Pottermore: Harry Potter and the Cursed Child
The theatre production opened in the West End of London at the Palace Theatre on 31 July 2016, with Anthony Boyle in the role of Scorpius Malfoy and Esther Smith as Delphi Diggory: Harry Potter and the Cursed Child, Parts One and Two