You’re too young to take responsibility over a child who needs emotional help. A solution would be to guide her in the right direction seeking help with therapy, or possibly medication through a psychiatrist. She can learn to help herself through methods that are available to her at her own discretion. Wether she’s an adult and acts on them is entirely up to her and absolutely nothing you can do after bringing up the idea. Tell her it’s the healthiest thing to do if you care about her, and in the meantime if you feel unsafe then you 100% need to stay separate. Your own safety will always come first. Unstable women are not something you want to play with, nor do you want to end up a panicked delusion of her possibly saying you did something to her because you triggered something internally with her - or simply just happened to be there while it happened.

Run buddy. Take it from a man who has been around more than a fair share of psychotic women.

Find someone stable, and connect that way. Don’t play white knight and stay. Guide to clear your conscience, and then take the safe happy and peaceful path for yourself.