Re-registering AFTER membership expires

Hello,
Re: S2Member Pro
I have a previous member (whose membership expired last month) who wants to re-register. When she enters her email address, username on the New Registration signup page, s2Member says something like: ‘this email address is already in use, please try another one’.
How do past members re-register so that the system recognizes them?
Reference link: http://www.aimcenters.com/registration-studio-level-membership/
Thanks. Karen
Re: S2Member Pro
I have a previous member (whose membership expired last month) who wants to re-register. When she enters her email address, username on the New Registration signup page, s2Member says something like: ‘this email address is already in use, please try another one’.
How do past members re-register so that the system recognizes them?
Reference link: http://www.aimcenters.com/registration-studio-level-membership/
Thanks. Karen