I think it's her universe and she just let's rest of us play in her sand box. I haven't read cursed child and everyone I've heard says it's not a great read and reads like mediocre fanfiction. So I get why the fandom is upset.
If I remember correctly, she didn't write it so it's basically published fanfictipn.
If I remember correctly, she didn't write it so it's basically published fanfictipn.