Question - I understand why you want her to do a no contact letter but really if you think that her stating it to you or showing you that she will be faithful is not significant enough why would this letter make a diffence? You state that you have no way of verifying that she contacts him or not if she does not do the letter. What if she does? What would stop her from turning around and contacting him to say my H just made me write that letter so I can stay in the house just ignore it.
I am not giving advice I am just saying perhaps you are getting too hung up on one particular item that may have worked for other people but may or may not work in your situation.
Me~34 H~38 D6.5
EA/PA-DEC.07
Moved out~Apr.13,08 Sep. Papers~Dec.7,08 No contact order ~Dec.9,08 and again October 13, 2009