Hi Cleo!
I just tried the email subscription in Chrome, and it seemed to work correctly. It looks like your daughter's subscription is currently pending meaning they haven't clicked the confirmation link sent to their email address. Can you let me know if they received the email?
I think the following may have happened:
1. She enters the email address and clicks subscribe
2. Some error occurred loading the confirmation page, which resulted in that error she saw
3. The confirmation email was actually sent but since she received the error, perhaps she didn't think it went through