To me, it is not beyond the realms of possibility that the child itself could be the focus of the acute psychosis: - if the mother is overzealously religious, they might believe it is "the Devil's child" or, if they've seen the relevant films, they might think it's an alien, about to eat its way out and, either way, they've expressed the intention to harm the child, the minute it is born.
I would like to know what was meant by the phrase "no mental capacity". If the patient has gone into complete torpor, failing to feed, drink, wash themselves then they obviously need something done about assisting with the birth.
If they are also unresponsive to verbal requests for permission to carry out medical procedures then the authorities are put on the spot but they have to take action, one way or another.
As for the fate of the child. I wonder if all its future adoptive parents will be suitably warned that its mother was bipolar and that there are variable odds of it having inherited the condition? I fear it may be in for a tough life.