In Jane Eyre by Charlotte Brontë, Eliza and Georgiana Reed act as foils to the eponymous heroine. As is the case with their mother and brother as well, they are antagonists to the heroine and illustrate two opposite types of character flaw.

Georgiana is a vapid young woman whose only asset is that she is pretty and blonde. She is devoted to a life of pleasure and self indulgence and illustrates the negative aspects of a lazy and selfish character with no concern other than immediate pleasure. Although Eliza Reed is more self-controlled than Georgiana and appears deeply religious on the surface, she is also mean-spirited and seems motivated in her religion more by jealousy and hatred than by love.

The two sisters appear at the end of the novel to show that their initial advantages of wealth and status were undermined by their bad characters. While Jane has a happy marriage and even visits Mrs. Reed's deathbed, the two sisters never transcend their fundamentally bad natures and do not achieve real happiness.

As children, Eliza and Georgiana Reed, along with their brother John, despise and torment Jane Eyre, their poor cousin. Their mother spoils them, dotes on them, and turns a blind eye when they are cruel to Jane.

When the adult Jane, educated, self-supporting, and self-possessed, visits them again, they have not done well in life. Although indulged and growing up amid wealth, neither is very happy in life. Eliza is a dried up single woman, and Georgiana is vain, lazy, and self-absorbed. They hate each other and attack each other with open spite. Eliza tells Georgiana that her life is worthless because all she thinks of is herself, while Georgiana accuses Eliza of sabotaging her marriage with Edwin Vere out of jealousy. As Jane puts it:

True, generous feeling is made small account of by some, but here were two natures rendered, the one intolerably acrid, the other despicably savourless for the want of it.

This adult encounter vindicates Jane.She is able to deflect their arrogance and refuses to allow them to intimidate her as they did when she was a child. She can see she is a better person, happier and more well-adjusted than either of them. This shows her—and the reader—that her deprivations in early life, from lack of love in the Reed household to the lack of physical comforts at the Lowood School, helped form her character, made her stronger, and equipped her for adulthood.

Eliza and Georgiana are Jane's cousins at Gateshead, the home of Jane's aunt, Mrs. Reed. As a poor dependent, Jane is constantly tomented by the Reed children, especially the brother, and heir, John. Eliza is the clever one; she is the one who instantly knows that Jane is hiding in the window seat in Chapter 1, while Geogiana is the pretty one, spoiled by her mother. Mrs. Reed says that Jane is "not worthy of their notice," because of her temper and her abilty at age 10 to stand up for herself. She is soon sent away to school, and we hear nothing more of Mrs. Reed and her family until much later,  in Chapter 21, when Mrs. Reed, on her death bed following the dissipated death of John, summons Jane from Thornfield. 

What we learn about these characters from this second meeting is that their lives have moved along a clearly defined trajectory. Eliza, "very thin too, with a sallow face and severe mien," has become even more flinty with age, seeking more than anything else to become a nun and be left alone. Georgiana, "a full- blown, very plump damsel, fair as waxwork," always the flirt, has become fat and made a poor marriage. In fact, Jane's return serves to show how far she has progressed, emotionally and spiritually, compared to her cousins. As Jane says, "Eliza did not mortify, nor Georgiana ruffle me. The fact was, I had other things to think about."