KAW, I think I know some of what you are feeling. It was maybe a month ago, by genuine accident (S9 needed a new notebook for school so I pulled one off the bookshelf), I found a journal entry my W had made, "I just ended my fifth affair on my husband .... I just want out of this fake marriage....".
I still get upset when I let myself think about the entry, but I have to remind myself that Journaling IS THERAPEUTIC. By writing confusing, emotional and complicated thoughts down on paper, it helps define them into manageable words. Not always 100% accurate, but manageable. Journaling also captures a moment in time and allows us to move past it, but in this case CAW has to WANT to move past it.
I think her comment about running into a brick wall is valuable insight for you to examine your DBing efforts. Why do you think W feels she is running into a brick wall?
I think leaving the letter where it can be found, but not actually giving it to you is just reflective of her indecision and confusion. DON'T PLAY HER GAME.
In wrestling, each opponent will have different style, and the loser is usually the wrestler that trys to react to their opponents style instead of maintaining their own. Same thing in chess - if your moves are in reaction to your opponent instead of in support of your own overall goal, you will lose. This doesn't mean ignore the other player, just don't change your overall game plan when they make a move.