abusive relationships

In an earlier blog this morning, I apologized to someone whom I am having difficulty simply conversing with let along entering into a friendship or relationship. She has been diagnosed with bi-polar. I am not sure she believes this diagnosis to be true. I am not sure she is regularly taking medication for it let alone on the journey to regulate the medication she is taking.
The issue is in a mere conversation this past week, we didn't see eye to eye on an issue so she attacked me verbally. I know who I am and am called to be, so I don't need to answer these attacks. But I did. And then there was some lucid discussion which spiraled again into attacks. I finally let her have the last word and I blocked her on face book.
How do you stay in relationship with someone like this? Someone who attacks anyone she cannot control or would have a different view point than she has. Someone who doesn't admit to her disease or the fact her disease effects how she perceives people. How do you stay in relationship with them, when every word you say is taken as a weapon? She reads her own paranoia into all conversations. How do you stay in conversation and relationship while not allowing her to abuse and use you?