I have been following your thread. Clearly, write the letter. Spend a lot of time on it. Make sure it is hand written on nice paper. It will make a difference. I also would recommend do some research on line on these types of letters to get some advice on what to say and what not to say.
It does sound like she needs space and time to see if your changes will stick. Just keep the changes going and put your W first over everything. I am not saying romance her but you cannot let work take precedence over her.
Me: 40, W: 40 M: 15, T: 18 D - 10, S - 7 D announcement 6/7/2014 A discovered 7/20/2014 (but denied by W) Still living together and sharing same bed