You know, I think the cliff analogy is very telling. Now you know with crystal clarity that your wife is dealing with a deep-seeded fear. Her anger, resentment, frustration and outright meanness are masks for this fear. (Fight or flight syndrome at its finest).
I'm going to caution you at this point on giving her questions that begin with 'why.' Why can't you... why do you... why don't you...
These questions will spiral into an argument in 10 seconds flat. A very big part of the problem is she doesn't know the answer to 'why,' nor has she taken time to figure it out. Understand that it is far, far easier to project problems onto your partner than it is to face our own fears.
Why isn't she willing to make an effort? Because there is an iceberg of fear inside of her and you and she are only seeing the tip of it.
When she starts throwing these types of analogies at you, trying to get you to see her POV, she is in panic mode. Understand that you are dealing with a very frightened animal, here. Asking her 'why' questions at this point, only compounds the fear.
You've scored a major victory is getting her to agree to MC. She will continue to try and derail you by trying to convince you that you are the one with the problem. You can reassure her, but not agree with her, by saying 'yes, there is most definitely a problem, and that is why we are getting help.'
Leave D discussions OUT of it. My shrink used to say to me, 'you can threaten to throttle your spouse, but never, ever threaten to leave them. The D word only increases fear and compounds the problem.'
Does this help you? No. And that really sucks because I know you are in sore need of some reassurance yourself. But... you have us, aren't you lucky. You are going to get through this. This is Huge Hump Number One. It's the hardest one to get over.