A Matter of Identity.
I was initially apprehensive that they'd extend her arc more than what I thought was necessary. However after seeing this episode and the amount of extra stuff they put in there, including the extra scenes that focus on her issues and relationship with Keima, I think I may have realized why the anime decided to do this, and it makes almost perfect sense when Ithink about it.
This realization is of course based on the current status of the manga content so it doesn't belong in this thread, but it arguably feels actually like a wise choice because it'll make the anime much clearer for viewers with no manga exposure, so I'll leave it at that.