Cannot retrieve password to old parental account to promote child Xbox Live account

She can log in on our Xbox but the Terms of Use appear and ask for the parental account email and password. Without this information she can't access Xbox Live, and although she is 19 now the Account tile on the Settings blade is disabled so she can't promote her account herself.

I know the parental email but not the password, and that email hasn't been used by its owner for years. I tried to reset the password using the account recovery form (entering as much information as I can from what I know of the adult) but all three requests have been rejected. I received an email to try again in 24 hours, but frankly that is all the information I can provide about the adult.

If someone could please help me with promoting my sister's account, I would appreciate it. Also, if it's easier, it would also help if I can replace the parental account with my WLID so I can bypass the ToU window.