Wrong Username Is STUCK On Admin

My wife tried to change the Username on the computer i put together for her. The only problem is that she changed the name somehow but it didn't change it in the OS. That is, when i go in through another user account it says the ORIGINAL name under users, NOT the name she made. Now the PROBLEM is that when the OS boots up it has her NEW name (that somehow didn't take), written in for the Admin account but the PASSWORD for the ORIGINAL account is the SAME (i.e. the password hint is the same as what i had made it originally).

Now the problem is that i can't change the USERNAME and there IS NO password for the name she made, cause it didn't take halfway through the process she said. The question is, how do i change the Username to the original name. that is, to the ACTUAL user name that is listed under users (the name she made is NOT listed under users).