Problem with the email linking of Virgin and O2

My mum has been forced to do the linking of O2 with Virgin for the emails but she's stuck at the bit where you have to enter a backup email address as she doesn't have any other email addresses.

It's no good her adding mine as by the time that I log-in to my emails any one time passcode will very likely have expired.

Is there a way for her to get around the problem as at the moment she can't access her emails. She doesn't have a mobile on O2 AFAIK, think her mobile is on Vodaphone.