Select your daughter's account, then View/Change ▸, Delete this account.
NB: be sure to delete the correct account and be aware of any email aliases linked to it as those will no longer be accessible.
FYI: if email accounts are not linked to an active broadband service account with Virgin Media or more than 90 days have passed since it was terminated then the account is at risk of being: (a) deleted without further notice; (b) not being recovered from a recoverable state that requires help from Virgin Media staff.
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