Was your sister working for you? If so, why? If not, how is this connected?
Also I'm not sure how the existence of a root user plays a part because on the vast majority of unix systems the default home directory permissions are permissive read (this was true in 1987 and is still true now) and if your sister didn't know about root users it seems fairly unlikely that she knew about chmod.
Also I'm not sure how the existence of a root user plays a part because on the vast majority of unix systems the default home directory permissions are permissive read (this was true in 1987 and is still true now) and if your sister didn't know about root users it seems fairly unlikely that she knew about chmod.