Judy Jones seeks self-satisfaction. Growing up, a spoiled child, she is accustomed to measuring things in terms of wealth rather than in terms of happiness. This is why she complains:
I'm more beautiful than anybody else," she said brokenly, "why can't I be happy?"
Although Judy is superficial and often treats Dexter indifferently, he idealizes and idolizes her as if she is some pristine beauty, glittering and unreal: like a dream. Judy is consistently compared to the illusion of a dream or daydream.
Upon hearing from Devlin that Judy's beauty has faded, Dexter's ability to dream in ideal ways and at least attempt to believe in their possibility is also gone. Judy had been Dexter's metaphor of superficial daydreams (like the one where he became a golf champion). When this metaphor is broken by the reality of Judy's fading beauty over time, Dexter loses the ability to care about such dreams.
When Judy invites him to dinner in Part II, Fitzgerald uses boating imagery in a simile (using like or as) to describe Judy's effect on Dexter. "His heart turned over like the fly-wheel of the boat, and, for the second time, her casual whim gave a new direction to his life." Dexter "was unconsciously dictated to by his winter dreams." Fitzgerald uses the fly-wheel simile to show how the dream of Judy affects Dexter; the same way a machine moves a wheel.
Judy is consistently compared to a dream, using metaphor or simile. In Part IV, when she and Dexter start seeing each other, she is described as "fresh as a dream" connecting two dream-like attributes: the illusion of her immortal desirability and the elusiveness of courting her without her seeing other men. A dream is, unless realized, like an illusion and until it is realized, it remains elusive.