User blog comment:Skysurfer92/Erza's durabi/@comment-2214433-20170323190627/@comment-30462872-20170323195515

Seems pretty legit to me, but I've got an even less logical yet entirely plausible theory. Irene turned into a Dragon before Erza was born and turned back, Erza could have been born with some of, maybe all the traits of a Dragon Slayer bar the Dragon Slayer Magic itself. It would be a neat twist, but probably won't happen.