I am in a very similar situation with my younger brother. I am constantly trying to help him so that he doesnt hurt others. I do not allow him to take advantage of me but instead I provide him the basic amount of support needed for an individual to survive. I will give him food if he is hungry and point him in the direction of a warm place to stay but I will not allow him to live with me or take my money. He does however, take money from my sick, dying father whom I have to repay for what my brother has taken. In the long run I feel as if I am constantly being affected by his bad decisions. He was also diagnosed Bipolar. Regardless of what he does I still have a heart for him because he is my little brother. But, I know I need to protect myself which means setting limits and bounderies to what I will help him with. I must also see he is doing something for himself.
I agree you need love yourself and don’t allow your sister to bring negative feelings to your life.