User blog comment:IamJakuhoRaikoben/Chapter 458: Morning Star, Review./@comment-26084508-20151027070737/@comment-7418318-20151027202615

That's because she was clearly hit.

The beam was trice the size of Ajeel's height and came not directly behind him, but slightly to the side.

While it's true that he most likely took far more damage than Erza, Erza too took some of the hit. And you can even see her badly hurt on the double-page.