Sounds like you are doing what you can. It's good you are working to improve your conflict resolution skills. WTG!
The only thing that popped into my head reading that was -- Maybe don't bother asking WHY it is a problem any more? Just let her solve it with her counselor.
Just accept it as it IS a problem. Then focus on management of the problem where it affects YOU.
So I am glad to hear you tackle that part like this:
I am going to ask her not to ask him any more and I'm going to ask him not to tell her and to request that she not ask him anymore as it's not her business. I don't ask.
WTG on that too!