User blog comment:Wrath022/Chapter 517: Wendy Belserion, Review/@comment-24039234-20170116172626/@comment-7418318-20170116182617

That would have been a way I would have been far more satisfied with.

Mashima could have said that in order to take the body, Irene forged a connection between her own body and Wendy's and Wendy just managed to first use this to get into Irene's body after being driven out of her own and then managed to use it again to travel back before it could fade away.

But even that would still leave Wendy's sudden ability to throw fireballs unexplained.