You know, of course, that friend will tell her all about "why" he no longer can have a "relationship" with her. Expect a verbal thrashing from your W about contacting OM. She sees herself through with the M and talk to any man she wants to.....and date any man she wants to date without your permission.
I don't fault what you did, however, it doesn't help all that much. You are right, she is very vulnerable to any man right now. But she will see any intrusion from you as "controlling". So, what would be another option?
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!