Thanks to Ashish Sondhi and Shika G for responding to my question of 13 March 2016 about Windows Live Mail.  Unfortunately they did not solve my problem because I had not described it properly.  I will try again below.

My wife and I share a computer. We each have our own desk top, email addresses, contacts etc separate from one another. We login to our emails on 'BTMail' each with our own password.  After deleting any unwanted messages we click on 'email' on our desk top and the remaining messages appear on Windows Live Mail.  We do not have to login on Windows Live Mail. When I was working on my wife's Live Mail (with her permission) I think I must have inadvertently clicked on  the tiny Live Mail icon at the extreme right-hand end of the top task bar.  In any event , the Live mail login popped up and demanded my email address and pass word.  Without thinking I entered these.  Now, whenever my wife goes to Live Mail this pop up appears, with my email address already entered.  The popup can be closed and disappears, but reappears whenever her Live Mail is re-opened. We want to remove it but don't know how, and are afraid that if we succeed we might affect my own email.