It is true that LBJ had the strongest motive to kill JFK, a fact obvious to everyone. Which is why LBJ insisted that Chief Justice Warren, a personal friend of JFK who also had twenty years of experience as a prosecutor, lead the investigation. That was LBJ’s way of declaring “I know what you are thinking, but I didn’t do it”. If LBJ had been behind the assassination you can be sure that J. Edgar Hoover would have been assigned to lead the coverup, not Warren and his blue-ribbon commission.
Not saying she did it - in fact, it's hard to fit spousal revenge into the known facts.
The trouble with most of the conspiracies is the premise: "He was killed because he was too good".
Most people angry enough to kill don't think the victim was "too good".