My daughter has a sub account of my account, but when trying to log on we get a
Message with no option, if I log onto my account I can't see her account.
Please advise.
TIA
Which browser and which device are you using to log on?
Are you using the "new" log on page
Did you "gift" the email account to her and did she set up her own BTID to accept the account?
See link and sub links about "gifting" an email account.
Creating BT Email addresses? | BT Help