Re-writing or re-inventing oneself is a particularly (post) modern habit, so I don't see Tolkien writing Morwen in any other way than to limit her to her original self-concept. And, anyway, isn't that part of the doom of the story, that none of the characters are able to rise above their own pitiful self-image?
So I personally don't see it as a class issue, but as a characterisation issue.
