User blog comment:Uraharattack/Ultear Return Debate Area/@comment-121.54.44.91-20160224060920

Well my theory of that was when Natsu and Gray are fighting the demon who possesses the curse of Time Regression ( I dunno the right term ) the one when you were affected by it you would become a child and When Doriate released his curse Ultear was near that time, and she was also affected by the curse and probably had the chance to return to normal.