Mrs Williams, whose 15-year-old son Kevin died in the tragedy at Sheffield Wednesday's stadium in 1989, had been suffering from cancer.
She was last seen in public earlier this week at a memorial ceremony held at Anfield.
She never accepted the original accidental death verdicts and twice took her fight for a new inquest to the European Courts.
Despite being diagnosed with terminal cancer in October, she was at the High Court of Justice in London to see the Lord Chief Justice Lord Judge order fresh hearings into the deaths.
Speaking after the historic hearing, which she attended in a wheelchair, she thanked Attorney General Dominic Grieve for being "a man of his word" in pushing for the new inquests.
She said: "I am glad we never gave up. It has been hard, but we wouldn't have been here today.
"I'd like a corporate manslaughter verdict in the inquest, it's the least for what they have done.
"God willing, I will be here, it has been a long wait to see justice.
"I am so glad I could be here today to hear it for myself."
Referring to the cover-up that shifted blame away from the authorities and on to the victims, she said: "I can't forgive them the extremes they went to. Why didn't they just give us the truth?"
Liverpool FC posted a statement on Twitter today saying: "Liverpool Football Club was this morning saddened to hear of the death of prominent Hillsborough campaigner Anne Williams. RIP Anne."