I read this book in middle school in 2000/2001. I don’t recall that it was a popular or extremely current book, as nobody else had chosen to read it in our class, but I don’t think it could have been written much earlier than the 70s; it seemed current enough, and the actual storyline was also somewhat contemporary.
I don’t remember much of the plot, but I believe the girl protagonist was an expat from the US living on the border of two or three European countries: I believe Switzerland (possibly Belgium, but I think she was located near the Swiss alps for some reason). She was going to this foreign school and I believe she didn’t quite fit in (not 100% sure on this detail). Pretty sure regardless that she was homesick.
The biggest recollection I have of this story is the feeling and/or theme: she’s quite lonely, and lives in a very in-between sort of place (because she’s literally living on the border of these two/three countries: I think Switzerland and Italy; if not, possibly her location was between Belgium, Switzerland and France).
The scene I can remember most vividly is a thematic description of the mountainous country surrounding her; she describes the differing terrains/ecosystems of the landscapes on each side of her: there’s a snowy, rough and high terrain (Swiss Alps?) and a (comparatively) more tropical, warm terrain (Italy?)