[jfengel]

There isn't a good answer to that question. The US had set a very arbitrary definition set of trimesters which actually worked rather well. The vast majority of abortions will happen soon after the pregnancy is discovered. Practically nobody who carries a healthy pregnancy past the sixth month will choose an abortion.

There is a lot of gray area in between, but not many cases fall into it. The previous US situation allowed states to put the dividing line anywhere in there, and that was a compromise acceptable to most. It's not a rigorously defensible answer, but the only rigorous answers are "all" and "none", and both are considered repugnant to most people.

A case like this is incredibly rare, and suggests mental health issues. For that, she should receive treatment. While there is an argument to be made that she should have the right to her bodily autonomy and terminate any pregnancy, it's extremely unlikely that this is what she would want if she were mentally healthy. So this case doesn't inform much about where you might draw a line, and more about how to diagnose somebody who is probably depressed or otherwise not competent.

I am not, of course, qualified to judge her competence. I can only speak in generalities.