She sounds incredibly insecure to me, like she needs validation of her importance all of the time. Think about it - feeling that everything is a slight against her when it has nothing to do with her? Basically, friend decides someone else's feelings are more important than hers? The truth is, that person's family WAS more important than her. She can't handle, with her insecurity, accepting that some people are just more of a priority than her.

The best way, I think, to handle friends like that is by making plans with her and then standing her up. When she reacts badly, you don't respond until later to follow up that she does it all of the time to you and how does she think it makes you feel? She will probably get angry about that, but it gives you a chance to measure your response. Heck, maybe she'll learn to piece her behavior and others' feelings togeher. Just talking about it with her clearly hasn't worked in the past. If all else fails, she doesn't sound like any kind of decent friend to me. Hopefully she will learn to grow otherwise she will find herself alone in short order.