Reset password for child’s appleid used in family share but is not supported

Couple of years ago my daughter and I were under a different family organizer and I need to switch her to mine. I sent the invitation, she received it and joined but we can’t get the email verification code because we forgot the password.

Her device was also changed from her appleid to mine because she continually defied my tech rules at home and got herself into too much trouble. Seems excessive but it was needed at the time. Now she’s 12 but only for a few more months and I’m trying to keep the account under control but using the appleid from the previous family organizer. What do I do?

I tried to reset the password but the error message not valid or not supported email keeps popping up! Any ideas?