User blog comment:IamJakuhoRaikoben/Chapter 287: Real Family, Review./@comment-3987368-20120615155806

Well, I have a theory.

Chelia is Sherry's cousin. Zeref's demon Deliora attacked Sherry's home. It's possible that she doesn't have Zeref's power but has something related to a Zeref demon. Heck, it may be Zeref himself. Can't know for sure yet...