Thanks for your thoughts on this. Ideally, what I want to do is to keep the same limited 3rd person, without moving from character to character -- but do it in such a way that it reveals more than the main character realizes. My reasoning is that for mood and characterization and some of the bigger themes of the story, the whole narrative should come through the viewpoint of the main character - the story is in a sense about her inability to get out of her own head.

In a way, solving the problem I described may end up being a fun technical challenge -- if I figure out how to do it -- but I may well end up adopting one of the solutions you've suggested.