In The Westing Game by Ellen Raskin, why might Judge Ford want to kill Sam Westing?

Judge Ford owes Sam Westing money she can’t afford to pay back. 

When Sandy McSouthers tells Judge Ford that there is smoke coming from the Westing house, she has a strong reaction.  He asks her if she believes in ghosts, and then tells her he is repeating what Otis Amber said.  She tells him Otis Amber is a stupid man, and immediately regrets it.  The comment was made because she is worried that Westing really was back. 

So Sam Westing has come home at last. Well, she could sell the car, take out a bank loan, pay him back—in cash. But would he take it? (Ch. 3) 

Grace Wexler wonders why Judge Ford is there.  She is a black woman, so Grace doesn't think she is a Westing heir since Westing was not black.  She decides the judge must be there in “in some legal capacity.”  She gets upset when the will is read and Westing refers to them all as nieces and nephews. 

Judge Ford does not like Sam Westing.  She says he was crazy when she finds out about the game and is insulted by the whole script.  She feels like it is another cruel trick of Sam Westing.  She says she will play the game as he would have played it—mean. 

The debt that Judge Ford speaks of is Westing paying for her education at Columbia and Harvard.  Her parents worked for Sam Westing as a maid and a gardener.  She used to play chess with Sam Westing, who constantly insulted her and won every game.  However, he sent her to boarding school, college, and law school.  He made sure that she got into the best schools.  She believed he did it because it was “to Sam Westing’s advantage to have a judge in his debt.”  

When she said all of this to Sandy McSouthers, who is actually Sam Westing, his response hints at the reason he might have paid for her education. 

“You’re awfully hard on yourself, judge. And on him. Maybe Westing paid for your education ‘cause you were smart and needy, and you did all the rest by yourself. (Ch. 21) 

Sam Westing may have insulted J.J. Ford, but he also saw something in her from a young age.  He taught her chess, and knew she was smart.  He paid for her education because he felt that she deserved it, and not because he wanted something from her.  As her presence in the game shows, he considered her family.