User blog comment:IamJakuhoRaikoben/Chapter 515: I Am You... You Are Me, Review./@comment-24367018-20161221184843/@comment-176.123.37.205-20161224095846

Perhaps Irene did not become a dragon the same way Acnologia did. Acnologia bathed in the blood of many dragons, therefore making him stronger and turning him into a dragon, whereas Irene did not bathe in the blood of dragons. As a result Acnologia can transform of will but Irene/Eileen can not. Juar speculation