You said you were "adopting the immensely arrogant position of the diagnoser" and I just wanted to say something about that.
Whether or not she was ever diagnosed, whether or not a professional would agree with your diagnosis ... whether she could be "proven" to have Aspergers or not -- you know what you know from years of a relationship with your mother.
Does she have it or does she not? You know that she has the traits that are markers for Aspergers and you know how that has made you feel all your life. You know that it has left marks on you, your expectations, you self-image, your relationships. And I don't think you are "arrogant" or presumptuous at all in calling it like you see it.
You are now enabled to see life in a different light, and be relieved of guilt for things you were not guilty of. It is OK to realize and to say aloud that it was not you that created this situation, but that you have the right and the ability to create something new and different for yourself.
I wish you all the best:)