User blog comment:IamJakuhoRaikoben/Chapter 493: The White Dragneel, Review./@comment-76.161.172.226-20160711151314

Mirajane fighting Juliet and Heine was a face saving measure for her. Her exhausting herself fighting those two, then getting caught by Irene makes her look strong, and simply had the bad luck to encounter Irene while she was out of power. If Mirajane had instead fought Irene and gotten stomped, it would make Mirajane look really weak.