KEB, What I'm going to say to you is going to sound really sucky but stick with me.
STOP trying to get her to see your side, or to see how you've changed or seen the light.
It will only piss her off more. Right now, she does not want to hear anything good about you..she is licking her wounds. I didn't want to hear a word my husband had to say and, moreover, I wanted to hurt him. Badly. I wanted to go for the jugular and hurt him..humiliate him, even..in the way he had done me. Until I got this out of my system I could not see any good in him. When he tried to defend himself or tell me he'd changed, it made all those feelings come back 10x stronger. I'd then go on the warpath again and want to hurt him, cause ALL I could think about while he was making those declarations was "Where the hell were you for the last four years?!?!"
When you write her letters, I think you should stick to her and how you feel about her. "W, you are sexy and desirable. I think you are a good mother. You make me happy with your funny jokes. I love the way your a$$ looks when you bend over to vacuum. Etc" LOL
Keep the focus on HER, and not on you. At all!!! I know this sounds terrible and you are longing to share your new self with her, but it is not the right time. She doesn't want to see the new KEB cause then she will have to shift her whole viewpoint and she doesn't want to do that right now. She is enjoying her pity party, in other words.
So here is my advice: Focus on her. Let your words be to and about her. Let your actions be for her pleasure. STOP trying to talk to her about you and your relationship with her. This will drive her away.
But I think you've got her wheels spinning. Keep the good parts of last night and repeat them. Ditch the rest. Repeat, repeat, repeat. Eventually you will wear her down, I promise you. I'm speaking from experience here!
