I don’t think the issue is you. The issue is getting the communication through, nothing more. If she is still in the “red zone” the message is dead on arrival. Let’s take an extreme example. Say you get in a fight with her and then in anger hand her the letter. Do you think it will have any impact at all, if she even takes the time to read it? So the next time you type up a letter, maybe in a month or so, how much impact will it have?
I think the one who is ready to give the letter is you, but you need to be sure she is ready to receive it. That was my only point, to get as much bang for your buck. Remember, patience works in YOUR favor, not hers.