Judge Ford was an intelligent woman who suspected that something was strange about the whole setup at Sunset Towers, including Samuel Westing's murder.

She thought it was odd that he should know in advance that he was going to be murdered and then set up an elaborate game to reveal the murderer. If he were really in that much danger, he should have called the police. They would have protected him and found the person trying to kill him. She also found it hard to believe Westing would use such a young, inexperienced lawyer to manage a $200 million estate.

Judge Ford felt that Sam Westing has planned some kind of revenge from beyond the grave. Since she had already been told that things were not what they seemed, she suspected the other people in the game had dark secrets. She made the decision to skip looking for clues and instead look for what each person might be hiding, trying to beat Westing at his own game.

In The Westing Game, why didn't Judge Ford believe Mr. Westing was murdered?

Judge Ford is the daughter of a servant in Sam Westing's house.  She grew up in his household, and often played chess with Sam Westing himself.  Judge Ford is familiar with the workings of his astute, calculating mind and his love for intrigue (Chapter 21). 

When Turtle tells Judge Ford that the "corpse" of Sam Westing which she saw the night of his purported murder didn't look like a corpse at all, but more "like a wax dummy", the Judge is excited (Chapter 21).  The Judge remembers that Sam Westing was in a terrible automobile accident fifteen years ago, and that since that time, "no recent photographs, no hospital records, no death certificate, just the accident report from the state highway police" exist.  Sam Westing was reported to have sustained "severe facial injuries" in the crash, and knowing that the man had been, among other things, a master of theatrical disguises, it makes sense that after the accident, he adpoted a new identity after having his face "remodeled by plastic surgery...a different face and a different name" (Chapter 22).

Unlike Turtle, Judge Ford never does figure out that Sam Westing took on not one new alias, but four.  After listening to Turtle's suspicions, however, she is convinced that Sam Westing was indeed not murdered, and was living on at least in the person of Sandy McSouthers (Chapter 26).