User blog comment:Yuri Rozu/Laxus Dreyar vs Mirajane Strauss/@comment-121.54.58.236-20160123040727/@comment-5894890-20160124190845

Regardless of plot, it'd be stupid if she could just use it on anyone. I would expect limitations on such power (as mentioned above), just like how Gemini can only transform into people within Lucy's magical power.