Hello, perpetuum, and welcome to Psych Central! How do you know if you are really the only one she has told all these things to, other than her giving you her word? I suspect she has told some other people.

You are a decent person to want to help her, but a friend is not going to be able to do so. As the other folks said, I think it would be best if you perhaps visit together now and then, if you can just keep it at that. She is not someone you will be able to get involved with in a healthy way. Sociopaths can easily manipulate people, even people they think of as friends. And, despite what you would like to think, you are no exception.