A third possibility is that Hazel lived
away from home, in a dorm or an apartment, for some time before moving back in
with her parents. It seems quite natural to me for a college student to
want to live in a dorm even if her parents live in the same town, and not at all
surprising for her parents to encourage or even insist that she do
so.
We know that Hazel lives at home, and other than her trip to
France, there is no indication that she ever did otherwise. She is clearly
living at home while she is doing homework, and fulfilling an assignment that
takes her to the Haunted Barn.
There is clearly something wrong here. To
make "roommate" mean Hazel's roommate you either have to re-write the
dictionary or the novel.