I think the “just” part of it makes it about her rejecting alternative identities, particularly in the context of looking over at the Skywalkers, and at the end of a movie where she’s a Palpatine.
If she had said Just Rey without looking over, that might be better, but the emphasis on the line in general gives it thematic importance that only makes sense with something for her to reject.
edit: ooh i like the just ben idea