Good god man! I remember reading your original post several months ago and couldn't possibly imagine that such an unhappy arrangement would work. Even in your original post you kept talking about "my" life instead of "our" life. You spoke of your wife the way I would a total stranger. The whole point of marriage is that you get to where you're going together. One person doesn't horde all of the resources for himself and leave the other to fend for herself, especially when it appears, by your own admission, that many of her problems are due to a mental illness. This was actually one of your quotes in the previous post: "How do I help someone who doesn't want to help themselves?" That's your WIFE, man!
I understand you have a child in this very unfortunate marriage, and divorce is always difficult for children. But at this point your primary concern needs to be figuring out whether staying in this marriage is the best thing for your child, not finding ways to cut off your wife who is suffering from mental health issues. You don't need dispassionate legal advise about a sleazy post-nup. You need to grow up and do the right thing by your child and the person you used to think of as your wife.