Subscriber stopped receiving email updates & can't resubscribe

My blog: https://veronicascornucopia.com. I have no idea what “version” of wordpress I’m using – I really don’t know much about the techy side of blogging – I just signed up in 2009 and kind of go with the flow.

I received an email from a long time email subscriber (I use the wordpress email subscribe widget) telling me she hadn’t received an email update since October 17, 2013. She has tried many times to resubscribe but never gets a confirmation email. When I search for her email address among my email subscribers, she is not there. She has old posts in her email from me so I told her to try unsubscribing with the link in one of the posts, and going to my blog to resubscribe again. Same thing happened, she received no confirmation email. Is there anything else I can do or she can do so that she can start receiving email updates again? I’m at a complete loss.