Yahoo mail failing to download to Apple mail

Several weeks ago yahoo made my wife change her password. That password change worked and she is able to get mail on her iPad and phone. She did not login on our iMac to get mail Now she tried to get mail on the iMac; now, however, yahoo mail refuses to accept the password using keychain on our iMac and yahoo refuses to accept my wife’s credentials to access yahoo web mail. Can some explain what is going on with yahoo?