Sometimes, suicide is something you carefully plan over a period of time. You put everything in place. You tie up loose ends, you write letters or time delayed emails and so on. You arrange to see people for the last time (although you do not tell them it's the last time). You give people things you want them to have. You make a detailed plan of how, and when, and you carry it out.
Sometimes, suicide is something that happens as a response to unbearable pain (or fear, or hopelessness, or any kind of mental/ emotional anguish), and there is no planning. It's like an explosion. It's what you realise you have to do, or what you realise is your only option, right now. You don't make plans, you just act. You might describe the feeling as wanting to die, or not wanting to be, or wanting 'this' to end, or not knowing what else to do but this.
Sometimes, suicides are accidental: you didn't mean to die. You did mean to harm yourself, possibly very badly. You felt real pain. You needed to escape that pain. You might have needed to show that pain and this was the only way you had (you think) to do it.
I have attempted. Obviously, I did not complete. I know what it is like to make the detailed plan (I know the way having the plan lifts your mood). I know what it is like to have the sudden need. I know what it is like to have no intention of dying but to go far enough with deliberate self harm that you are risking it.
I know that no one is responsible for my mental health, no one has an obligation to listen to me talk about it, no one has a duty to support me, no one should ever, EVER, have to prioritise my feelings/ wellbeing/ needs above theirs. You are allowed to draw back from your friend- you're more than 'allowed', permission doesn't even come into it. Your friend's agony is horrible, their suffering is awful and so very sad, they have a right to support and care and love and the attention they need- but you do not have a responsibility to provide it and their pain does not in any way reduce your right to protect yourself.
You don't have to fix her, or anyone else. You matter as much as she does. You aren't obligated to soak up her pain and be her support ad you will have done nothing wrong- honestly I cannot emphasise this enough- if you need her to stop bringing this to you.
(And if my post has in any way upset you or made things worse, I am very, very sorry).