This is a hard situation. You have the right to set limits and boundaries with your friend. After being honest about the effect she is having on you, you can say "I can't engage in this topic anymore until you do x"---an ultimatum if needed.

It means being willing to lose a friend which is scary. I lost a friend this way but in the end it saved me from a very toxic relationship. I emphasized that although I can listen and be supportive, in the end she needed treatment which she refused to do. I was caught up in a bad dynamic where she wanted me to take care of her.