We know that Jack Thorne wrote a play called Harry Potter and the Cursed Child with JKR's approval, and that Rowling claims to have given the creative team access to all the material she had prepared on the characters.
What changed your mind?
J.K. Rowling: Meeting Sonya Friedman, Jack Thorne and John Tiffany changed my mind.
I knew there was other material there, I gave it all to them and they've turned out the play
With this in mind, are there any specific elements first revealed in the Cursed Child which show signs of having been foreshadowed by Rowling in her own writings?