I would let the counselor lead the way. That way, your wife will not feel blindsided if you use it as an opportunity for some marital counseling.
However, if and when the counselor brings up your relationship with each other I would not sugar coat. Tell her that you've been unhappy for years and your wife has been unresponsive. You have nothing to lose, is my thinking.
Sometimes hearing these things said out loud to a third party has a VERY big impact on the uncooperative spouse. I know that when I talked to our parish priest about our situation, my H shaped up pretty rapidly after that. Not that the changes stuck around permanently, but it did have an immediate effect on him. Sortof like his 'cover' had been blown, is the best way to describe his behavior.
Keep the focus on your daughter (who I hope is going to be ok, btw) and don't shy away from any pointed M questions. That way, you will have accomplished two things--most importantly you attend to your sick child, and secondly you refuse to play your wife's "bury your head in the sand" game.
