That was, evidently, my misinterpretation of the rolesheet. I thought that "needs to kill one of thier own every third night" implies that the Unstable person would have to know who their teammates are, and thus could only be a wolf.
Unless I also misinderstood "can not choose themselves". I thought this meant that, if I was Unstable, I would not be able to suicidally kill myself in order to prevent further damage to the rest of my team. However, Sora may have meant that the Unstable person would not be able to choose their own target at all; rather, Sora would choose a random target from all the players on the same team as the Unstable person and zap them on the appropriate night, in which case the Unstable could easily be a villager or a Cultist.