Besides what others have said, in reading I had to wonder if this is her behavior on a regular basis or episodic. If it is an all the time thing, you may be dealing with a personality issue as well (we can't diagnose of course, just that with bipolar, it wouldn't be a constant). Has this been how she is since you've known her? I have to wonder about drugs too. People can be very sneaky, I know from first hand experience of not knowing for many months that someone very close to me was using.

Best of luck to you.