My sister knows this woman who has borderline personality disorder, and this description fits her right down the line. She was originally diagnosed as bipolar, but she doesn't have the depressive mood swings.
She went back to the mental hospital a few times and finally got the borderline diagnosis. She's impossible to deal with when she gets off her medication. She tells these fantastic lies about people, harasses them on the phone and does other things that have pretty much isolated her from having too many friends. People get tired of dealing with her extreme instability.