Omg, are you serious? Jesus, I think you should call the hospital or emergency services if she's going to do it, get her some help. Suicide is never a good answer.
Call the suicide hotline wherever you are and get your friend some more professional help. I appreciate that your position is difficult to be in, but in this case the path is clear.
I was hoping for a less brutal hanjie after reading the description. Having (less severe) mental health issues myself in the past I totally understand your friends viewpoint and the pointlessness of day after day of suffering, but as a friend I'd have nothing to do with helping someone die, and I think/hope I would phone for help for her, unless she's very elderly.
I used to be really depressed and have also thought about suicide. I also tried medication, and therapy, both of which didn't work. At the time I couldn't imagine being happy, and if I were happy, then that wouldn't really be me. I guess I still have some of the thoughts I used to have, my opinions haven't changed much (thoughts about how messed up this world is, how pointless stuff is) but I've "come to terms" with them. There are a lot of little things that I enjoy. I'm ok with the person I am. Being depressed can sometimes make it feel like everything is being smothered is sadness or apathy, but sometimes there are still little things that can be enjoyable (sitting on a bench in the Sun, drinking a beer). Maybe try to help them find those things, or encourage them to find them. You only get one life, you might as well live it, even if some of it is sh*t.
What a dreadful position to be put in - how awful for you. Here's a link to a worldwide list of suicide helplines - please ring one asap to talk this through and get some professional advice and help: www.suicide.org/international-suicide-hotlines.html Also be aware that in many places, not helping save someone who has e.g. taken an overdose, is illegal and you could be prosecuted if you are there and do nothing. Wishing you the very best.
I don't think this is the right platform for such questions. There are surely other ways, more serious ways to find advice. I understand your dilema, but this is definitely not the right place. You can even find better platforms in facebook.
Hope your friend finds the help she needs, one way or the other.
Thank you very much for all the advice. I'm sorry if I upset people by putting it here rather than a suicide/depression forum. I didn't post it on the suicide/depression forum as I knew people would either come down strongly on either side. I wanted a neutral forum to see if I was thinking irrationally by even considering my friend's request. It is most definitely my friend rather than myself and since posting this the decision has been taken out my hands temporarily. My friend is currently in hospital after causing severe friction burns to her lower arms. So at the moment she is in a controlled environment. She is however not being honest with them and has stated she is not suicidal. Following the advice from you wonderful people, I intend to make the hospital staff aware of her request to myself. Thank you again - I thought I might be being unfair to her request due to her history and part of me almost thought it was justified. It's amazing how much things can get out of perspective.