User blog comment:Miskos3/Fairy Tail 514: Dragon Seed, Review/@comment-24784846-20161213010900/@comment-7418318-20161213063529

With enchantment she can change pretty much anything, including bodies. Maybe she altered her own body so that Acnologia wouldn't recognize her as a Dragon Slayer.

Or she somehow managed to reverse her state after the first symptoms showed and is no longer a DS... but that would beg the question how she survived for 400 years.