User blog comment:IamJakuhoRaikoben/Chapter 515: I Am You... You Are Me, Review./@comment-117.223.154.228-20161220220753/@comment-7418318-20161221081655

To add to what Wrath already said: She was flying around freely for around 400 years before Zeref gave her a Human body. So even if the body-changing changed her scent to something that Acnologia doesn't recognize as a Dragon, there still a 4 centuries long plot hole right now, so to say. ;)