Hi, I'd like to help you with your question.
First I would like to say how sorry I am that you have suffered such a loss. It must be devastating to have lost not only one child but two. My condolences to you.
After reading your description, I have to say that you pretty much have answered your own questions! You seem very insightful and right on target about your former friend.
All of the things she said and did to you were cruel and uncalled for, no matter how she felt about your situation or any attention you were getting as a result. You are right, sometimes people do say things during crisis times or other times of loss that are wrong and thoughtless. It happens. People often do not know what to say and say the wrong thing. However, your former friend repeated these hurtful comments and then added cruel actions on top of it. That is not someone making a mistake, that sounds very intentional.
I think you did the right thing with ending your relationship with her. It sounds like she would just continue with her behavior and you would only continue to get hurt. When we have something so horrible happen in our lives, we need our friends and family to pull around us and support us through it. It appears that your situation brought out your friend's true colors and the relationship did not survive as a result.
It is hard to say why she did what she did. I think you listed some very valid possibilities as to why she acted this way. Since you mentioned that she has always had appalling behavior, then she may very well have a personality disorder. Some people cannot stand the thought of not being the center of attention and this may be her way to try to get you out of the spotlight. She may also be extremely insecure and need to pick on others to feel better about herself. No matter what the reason, there is someone wrong with your former friend and it sounds as if she could benefit from therapy, if she was willing to get help.
Again, I am sorry this happened to you. I hope you have a lot of other supports to help you through this difficult time. If you feel the need, grief counseling may benefit you. There is also a place to get additional support called The Good Grief center at http://www.goodgriefcenter.com/. If you do not know of this place already, they are highly recommended to help families and friends through the grief process.
I hope this has helped you. Take care,