More, your family and friends. In any personal case of someone I don't know, I should have no say whatsoever, unless you involved me for some reason. If, for example, you told me of your plans, then I think I would have good reason to try to dissuade you and to help you. Otherwise what I would say in your case has no weight at all.
You still haven't really elaborated under what circumstances you would "coolly and rationally want to kill yourself". While you don't have to share these if you'd rather not, it makes it hard for me to really respond. Would you kill yourself, coolly and rationally, if an exam went wrong? More reasonably, would you do so if suffering from daily pain? Perhaps in response to a family tragedy... and so on. I can't speak in general terms. I only know that in my specific case it would have been irrational, and I don't see why it is so controversial to say so for this woman either. Taking the circumstances at face value she appears to have over-reacted. Therefore, I can only assume that there is more to the story. Most likely, again based on my own experiences, she had lost perspective due to mental illness.