Since the N-400 asks for places of study, the interviewer will see she is a student and may ask about the dorm arrangement. But she doesn't need to voluntarily say anything about the dorms, nor does she need to list the dorm address unless specifically asked about it. No need to take any extra address page; she can just give a verbal explanation if asked and it won't be a problem -- the interviewer will just write a note on the application if they care about it (and they almost surely won't care). By default, for almost every legal purpose (taxes, driver's license, voting, immigration) the residential address for full-time college students living on campus and being supported by their parents is considered to be their parent's address unless the student takes action to claim otherwise.