Yes Fauna will have to move out. In fact, she might have to go through the 16 villager cycle so that she can move into your town again! :c It may be awhile until Fauna can move back in, but I'm not totally sure myself. I would really look into it before moving her out, I'd hate for you to be without her for too long. But I'll be around if you need me to re-cycle her! I don't mind~