This is crazy! ... Like I wrote earlier, she sounds unhinged. But maybe that's good. People with serious mental health problems often need to hit rock bottom before they will consider getting help. Maybe this is her rock bottom, and she is, reluctantly, willing to get some help.
Or she may just flip flop again.
I think I would see if you can meet with her when she's in a calm state of mind, somewhere new, somewhere quiet and calming -- somewhere other than home. And just see if you two can just converse reasonably, and see if she can reiterate/articulate better what she's thinking. You would just mainly listen. I'd probably do that before taking her up on her offer to go see an MC.
It seems to me that the real root of the problem is your W's mental health, and the ideal situation is one where your W gets help for herself first, before tackling your marriage. But I'm guessing your W isn't willing to do that at this point. In that case, I've been advised by counselors that it's OK to get that person into MC, and if the MC is any good, the MC will gently guide that person into individual counseling.
I'd ask your IC for some advice. I don't know how much regular DB techniques apply when your spouse is not in good mental health.
Like JRuss posted, I'm watching your hurricane on TV, while in the eye of my own hurricane.
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final