A classmate 1 let classmate 2 log into the website using classmate 1 computer, now classmate 1 cannot get her e-mail thru CC she is advised that she has to log in using classmate 2. How do we fix this problem?

It sounds like "Remember Me" was checked, so that Classmate 2 is being remembered. It should just get fixed when classmate 1 goes to the website and clicks LOGOUT. This will log Classmate 2 out and so Classmate 1 can enter her login information again.

If not, it for sure will get cleaned up if cookies for the browser are cleaned up.