This is one I really had to sit with a bit after finishing. For such a quiet film with such a simple arc, it's got so many angles to it. I read it first and foremost as a portrait of alienation from the world, Carol's disease as a physical manifestation of a spiritual sickness, an allergy to the falsehood and unreality of the world around her. But it's also easy to think about disability justice readings, feminist readings, even queer readings of the transition from a world that rejects you to a world that is outwardly positive but totally fails to address the same structural issues.
It's that transition midway through the movie that makes this truly brilliant and multidimensional. When Carol moves to Wrenwood, this goes from being a simple parable about chronic illness to a much more complex and toothsome look at people and structures and the way the one exists within and is shaped by the other. The film meticulously avoids moralizing while making it clear that this change is not helping, and that subtlety carries it incredibly high.
I really need to rewatch this, I think.