In this photo, Betty holds a drawing of a smiling blue whale with three harpoons embedded into its body.
After seeing a contented Don’s love note to Megan, Betty’s desire for revenge leads her to hurt him through their children, of which there are three - in this case, Sally specifically:
Captain Ahab’s (Betty’s) revenge-line as he throws his final harpoon (her reveal to Sally re: Dick Whitman) at Moby Dick (Dick Whitman):
“…to the last I grapple with thee; from hell’s heart I stab at thee; for hate’s sake I spit my last breath at thee.”
—Moby Dick, Chapter 135. “The Chase —Third Day”
Ahab’s neck gets looped by his own rope and he dies a victim of his own obsession with revenge; symbolically what happens to Betty once Sally discovers her mother’s twisted action.