For this question, I believe Albus has 3 strategies: N, E, and S, and Minerva has 8: aaa, aab, aba, abb, baa, bab, bba, and bbb. I've also found the rollback equilibrium to be the case in which Albus chooses N and Minerva chooses b. However, I'm not sure how to represent this equilibrium (equilibria?).
Do we say that the unique equilibrium is simply (N, b), since those are the choices made by the players, or do we say there are 4 equilibria: (N, baa), (N, bab), (N, bba), (N, bbb) since Minerva's choices are in reality a set of strategies, all of which result in her choosing b in response to Albus playing N?