Actually I see nothing too terribly wrong with your response, especially if his goal is to use the correspondance in a custody trial.
You made a point to be repectful of the fact that the both of you being both her parents care for her.
Fact of the matter is, whether in happy times or times as such, I'd love to see a family unit where BOTH parents handle a situation exactly to a 'T'. We don't. We were raised differently by our own parents and thus, do what we know.
I wouldn't lose much sleep over it. It's unfortunate, but as I've learned, even after the D war is "over" and there's no sense in dragging issues out between yourself and X, their hostility lives on through the kids. When will it stop? I don't know, I'll let you know that one when I do myself.
Me 35/XW 33 S13 & S12 M: 10/17/98 OM & S: 07/08 D final 06/09/09 12/03/09 - 06/13/10 "Piercing" 06/13/10: Engaged to Re-marry 10/17/10 06/25/10: Expecting baby #3 2/14/11