I totally understand how the moments of validation, acknowledgement of the same reality from your sister were very important and healing for you, Tupp. I think what that is, is "I HAVE A WITNESS."
I have felt the same way on some small occasions with friends, who had observed my mother and got it about her self-absoprtion. But the biggest events were:
1) When a judge, in a courtroom, said NO to my abusive brother, who is so beyond N as to be sociopathic
2) And, very ironically, when my mother herself dropped her denial of his abusiveness to me, just for a few golden moments in a nursing home garden. She acknowledged that he had always, always hurt me, and said, "What is the MATTER with that boy?" Sadly, it was her own genes, most likely, that explained a lot of him. But having her say that, confirming the reality I experienced as a little child, was enormous. In near extremis, and at 98, she was able at last to speak that truth out loud.
I am glad your sister came, for what that gave to you.
xo
Hops