Resubscription Confirmation Email not received

Resubscription Confirmation Email not received

One of my contacts unsibscribed from our newsletter by mistake. She tried to resubscribe, and the system said to check her email for a confirmation, but nothing is coming through. I need to add her back to our mailing list but the system has flagged her email address and will not let me add her back and she is also unable to add herself back. HELP!