She and the granny want to keep the baby and grandma has said she'll take the child on. Can't see what's wrong with that when it boils down to it
Except she can't keep the baby, for the baby's safety. And people who know a hell of a lot more about it than you do can see what's wrong with it.
I don't think the state has the ability for legitimacy to decide mental "capacity"
The state doesn't decide, doctors and the courts do. Are you really incapable of understanding the fundamental principle that the courts are not the state?
I am against state enforced medical intervention too. People should be allowed to die if they want to, not kept alive to be tinkered with by medics while they progressively lose quality of life.
Again, if anything it's court-enforced, and only if it is demonstrated that it is in the best interests of the patient. There have been a number of high profile cases where it went the other way, and the courts have ordered that medical treatment be withdrawn whilst relatives want the patient to be kept alive whilst progressively losing quality of life. Is that wrong also?