I'm with Cathy. How can you turn "her move" to your advantage? It is your move, and you can't keep passing forever.
Do you want her to start a conv about the letter - move it so she knows you put it there. Do you want to start a conv about the letter? Either bring it up yourself, or take the letter and hand it to her when appropriate. Do you want the whole thing to "blow over" - clean up the pile of stuff the letter is buried under/on top of and make sure the letter is visible inside a trash can. - this one is risky if W may interpret this action as discarding her, and not just the letter.
Or draft your own letter, journaling your thoughts and goals - NOT A RESPONSE/DEFENSE to her letter - and fold it inside of her letter.
Life is a game, we either play or watch - I choose to play.
