Unfortunately, what you are describing is all too familiar. There are individuals that "carry the hatchet" and often as is in what you are recognizing "THEY NEVER LET IT GO". It's often, as you are describing, a waste of time to talk to a person like this who simply will NOT let go of their "hatchet".

I have an older sister that is EXACTLY like what you are describing. And she got worse and worse as she got older. In fact, it's gotten so bad it's embarrassing for me when others are around to witness it.

Let your brother handle it, maybe he really does deserve a medal for taking care of her. The best thing to do for your own mental health is to limit your exposure to her. It's a waste of time to try to point ANYTHING out to her either, as you have experienced all that results is how she wields her hatchet at you.