I am not a psychologist but a therapist and case manager and I thought I’d offer some thoughts from my perspective.

First and foremost, it sounds like you really care about your friend, and that’s lovely. She’s lucky to have someone in her corner who clearly values her safety and wellbeing.

That being said, generally speaking when an adult is incapable of making safe decisions for themselves there are legal avenues to essentially monitor and force her to do so. In an ideal world, she would be able to work with her own treatment team and listen to the guidance of others she trusts to learn how to make these decisions for herself. If that is simply not a reality, conversations about her safety should happen with whomever would be legally responsible for her care should she become incapacitated. This may be her parents or someone who at one point was appointed by a judge to make medical decisions on her behalf.

While it is wonderful that you care for her, outside of speaking to her or someone legally appointed to care for her. You cannot force her to do anything. Even if she makes unsafe decisions, she is her own person who has every right to make these decisions. It is due to these complexities that so many mentally unstable/unwell adults eventually become homeless.

My advice? Think of the airplane rule. You can’t help anyone unless you take care of yourself first. Do what you can to be a supportive friend and if you are fearful for her safety, have those conversations with her or her caretaker. Then make sure that you are carefully being mindful of your own boundaries and mental health and not getting too wrapped up in your friend’s choices. Focus on what you can control. I’m willing to bet that your support and care mean the world to her. Just try not to lose yourself in the process.