Recently very hurt by a friend

Not going into the gory details, but a few are necessary. Sure would like to know what others think of this situation.

I had, HAD being the operative word, a friend who was frequently needy. I think that she didn't always realize just how needy. She was ill and her illness was debilitating, however she rarely acknowledged this even to herself. She didn't like talking about it and resented anyone including me asking questions. On the other hand she would frequently become very angry if I didn't ask or didn't somehow acknowledge her illness in conversation.

Some background: At one time she worked for me which is how we originally me. We became friends and I really enjoyed her personality and wit. It was a pretty rough time at our employer and several months after hiring her I realized that her illness was creating difficulties for her in her work life. I protected her, she didn't realize this though and continued to pretend that she was 100% and everyone was simply refusing to acknowledge her contributions and commitment. Things ultimately spun out of control at a time when I could no longer protect her and she was fired, it was not a "good" firing but that is a different issue.

We remained friends, but it was often a difficult relationship. She would frequently chastise me for my style of communication telling me that I was to dispassionate or clinical. That I didn't "give" her enough time. That I would hang up and not call back. This was after hours on the phone with her. She wanted all my time and resented any time I spent with my husband, at the gym, or anything else. She couldn't take honest critism, didn't want to hear anything other than agreement with her sometimes very off the wall fury at me or others. She frequently torpedoed herself in her job search.

This past week was the final straw. I lost a good friend last weekend. I didn't call her instead I simply dropped her a e-mail apologizing for my lack of communication and explaining that I had lost a good friend. She went balistic. I was all kinds of insensitive, I was a user, I was everything under the sun. Needless to say I was really hurt. I tried to talk to her. I have bent over backwards for this woman time and again, including loaning her money ($3500) when she really needed it (no she hasn't repaid it).

The end result of all this is that she has decided that I am a bad friend because I was unable to make the changes to my personality that would accomodate her needs. I couldn't give up my life and spend every free moment I had on the phone with her every day. I didn't do everything she wanted me to do everytime she wanted me to do it, no matter how unreasonable it was. Her fury escalated so quickly and beyond anything I had every seen before. I don't understand it.

Sorry for the length of this, there is plenty more but I tried to keep it as short as possible. Should I be worried? She does have the ability to do harm to me professionally and personally. What would cause someone to act this way?