Unable to delete user account

I set up a standard user account for a daughter on a MacBook a day ago, but I made an error setting up the password, cannot remember exactly what I did and now cannot access the account. Nor can I access it from sys prefs/user & groups using my admin account and admin password to unlock it and make changes. Though unlocked, the pane does not allow me to select her standard user account (presumably because it is password protected), so I cannot click on the "-" and delete it.

Can anyone advise how to delete her user account, or change the password on it without knowing the old one, perhaps using terminal commands if necessary? Thanks.