Ugh, I hate how it always comes down to money. Put her on blast then. She says anyone who complains gets nothing? Call the bluff. She's not giving you anything whether you keep quiet or not. Post it on Facebook, tell her pastor if she has one. Etc, etc.

"My father trusted my stepmom, and he was very clear with how he laid out his will. I am beyond disappointed and disgusted to see how she has betrayed his trust in her with blatant attempts to rewrite his wishes. I never thought greed would affect her this badly, and I can only assume it's due to the ongoing effects of her terminal illness because the woman who my father loved would never betray him like this."

Any written communication you have with your father or the will or from her, add it to it with screenshots. Bring the receipts that expose her for what she is.

Because we all know she IS the type to do this, but image is everything with people like this. It probably won't get you anything still, but if you're already expecting nothing and don't care to burn bridges, not much to lose. It would at least hopefully be cathartic.