In Aldous Huxley's "Brave New World," Fanny Crowe is a Beta who represents the conventional thinking of her caste.  In Chapter 3, she scolds Lenina for only dating Bernard and not being promiscuous:

'But one's got to make the effort, one's got to play the game.  After all, every one belongs to every else.'

Later in the novel, Fanny encourages Lenina to make sexual advances upon John the Savage as Lenina talks to her about her emotional feelings towards John. A static character, one who is never fully developed, Fanny acts as a foil to Lenina who has some urges to break from the conventional behavior of the New World.

On the other hand, Watson Helmholtz, an Alpha Plus of extremely high intelligence, is in sharp contrast to Fanny.  For one thing, his character is well-developed and he displays an independence of thought and rebellion against the New World.  Like Lenina, he is disastisfied wit the mindless recreational sex of his society.  In fact, he abstains and saves his energies for what he feels are more valuable activities, such as writing anti-social poems.  In his rebellion, he aligns himself with Bernard, but Helmholtz proves to be a more serious rebel that Marx who, after finding the Savage, seeks to ingratiate himself with his superiors, and who complains and whines, breaking down when Mond serves him the punshment of banishment while Helmholtz welcomes his banishment as an opportunity to foster his creativity.

Perhaps the only parallel between Helmholtz and Fanny is that they are friends of two people who are not conventional for their caste, Lenina and Bernard.  And, they act as foils to these two semi-developed characters.