Why Couldn't Sable Add 2+2?
A) She knows something is going on between Frankie & Jason
B) She finds a letter from Frankie's husband Phillip, Jason's brother, saying Frankie's unborn baby (Jeff) isn't his
C) She knows that at the time Frankie became pregnant, she and Jason were both living under the same roof
Despite all of the above, it doesn't occur to her that if Phillip isn't the father, Jason is the most likely candidate. Instead she drags Jeff into court to prove he isn't a Colby and had no right to be given Constance's stock. And is totally shocked when Jason winds up declaring he is Jeff's father.
For somebody who was supposed to be smart, that was a truly dumb move.