This is not easy, SnowCode, and there are no methods that would guarantee she won't act on her thoughts. Having said that, having suicidal thoughts does not necessarily mean she'll commit suicide. But it most definitely means that she is hurting a lot.

What might help is to get her to talk about what bothers her and validate her feelings (don't suggest 'solutions', but say something to the effect 'that's really hurtful/abusive,' or even things like: 'I can't imagine being in your situation, I'm so sorry you are going through this.' -- or even, get angry on her behalf, if that makes sense). Alternatively, if she doesn't want to talk, offer to share some of your hurts and traumas and see if she's willing to hear you out (I know this sounds weird, but the point is to connect in some way and some people find it more soothing to listen than talk).

Ideally, this should be done in person or at least through a phone; text chat is really not a good medium for this. But mind you, whichever way you do it, this is incredibly difficult. People in this state tend to be irritable (to understate it) and it often seems that no matter what you say, you are making things worse. However, as long as they are talking, whatever you are doing is working. The aim here is not to 'heal' them, but to help them to calm down. Ultimately though, there's only so much you can do.

Personally I find when people try to comfort me when in a predicament where death is genuinely better I find almost everything people say to be condesending. So just listen and make statements that confirm people's feelings and show that you are listening.

For example if they say X makes them want to kill themself you can say yeah, I can totally see how such suffering would make you feel that way. If they want something they will ask.

Also to give methods behind my statements I actually have been trained in how to talk to people who are like 1 hour from killing themself and usually less severe situations. So I've had a shit ton of practice and I can tell u from experience that my advice is decent.

I would be more concerned about u setting healthy boundaries tbh. Letting a depressed person drag u down and take up a ton of emotional energy almost is never healthy or helpful to either party. The amount of times suicidal people try and cope by trying to be abusive or manipulative is super common. So if u don't think u will be able to set boundaries or feel like boundaries are being pressed be okay with ditching the friendship.

the most important thing to remember is that it's not your fault if you can't help her. Beyond that, if you feel like you have the time/energy to try, I'd talk to her privately about setting up somewhere for her to go so she's not stuck at home with her parents (like an aunt or uncle, friend, teacher, or if it has to be... a woman's shelter)

When I'm dealing with strong ideation and a desire to attempt the thing that I need most is someone to just listen and affirm what I'm feeling. Making me feel guilty about who I'd leave behind isn't helpful because when I'm in that moment I believe that they're worse for knowing me and would be better off, so anyone saying otherwise is just lying.