For the most part, this is on her to figure out. And as much as you want to show support, you are very limited in what you can do. I think I have asked this before but can't remember, has the C explained to your W about the withdrawals, doubts, confused feelings, and fear of uncertainty? Has she explained this is all normal and has nothing to do with love for the OM?
Some of the details, time slots, etc., during my withdrawal is a little fuzzy after all these years. Of course I don't dwell on it, so that may be why. I remember how I felt and the depression and panic attacks, etc. However, I did not talk about feelings for OM to my H. Just b/c that's what I did is no measuring stick for another WW, I'm just expressing thoughts here. I read a lot of books, and it helped me cope. I still had weak moments, but I was able to comprehend what was happening to me, once I received the information. However, if I had not cut all manner of contact with OM.........I could be telling a different story. It would have been a lengthy emotional hell to endure. In that regard, I can feel for your W. I was told right here on the board what was coming, and AmyC (former WW) & imlyn (former LBW) held my hand a few times off the board. So, yes I understand the need for support.
To me, it just doesn't seem right for her to discuss her feelings about OM to you, and for sure, not verbally compare her feelings for you with those for OM. It may sound crazy to say it seems disrespectful (considering how disrespectful an A is) but it continues to inflict pain on you to hear this. Would it not be better for her to meet with the MC alone a few times, rather than continue to rehash this with you?
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!