User blog comment:IamJakuhoRaikoben/Chapter 372: Breach, Review./@comment-2214433-20140221152105/@comment-7418318-20140221161518

Hey, here's a nice thought: Mira has already moved away from the lab, leaving Lamy behind (either because she didn't seem like a threat or knocked unconscious).

Lamy, hearing Lisanna call for "Mira-nee" jumps Lis and turns her into a Demon to get revenge on Mirajane for busting one of the tanks and spoiling her fun.

Of course the timing would be a problem, but maybe they have a faster, though only temporary way to demonify someone. Or something like Walter's vampirification in Hellsing, which was a quick and dirty hack-job and ended up with his powers going out of controll and him being destroyed by them.