Debbie keeps getting emails from people saying that they can't open the attachment she sent. Is she being spoofed? Leo says yes. It's very common and unfortunately, there's nothing she can do about it except wait. Eventually, the spammer will move on to another email, and they'll go away.
Leo recommends setting up a GMail filter to route those emails to the trash. Then at least she'll never see it. But if in the body of the email, someone is impersonating Debbie, then that means she's been hacked and someone is using her Gmail account. She should change her password immediately. And in the bottom of her webmail, she'll see an 'account details' link. That will tell her how often she was hacked and from where. Debbie should also turn on two factor authentication so it's much harder to hack her email account.