Myrtle (and her husband George) represent the lower classes. They live in the 'valley of ashes', an area literally and symbolically impoverished, a great contrast to the luxury of the mansions of Long Island. George tries to imprison her when he learns of her infidelity, and it is in her attempt to escape that she is killed.
Myrtle is described as having a raw sexuality, perhaps something that wouldn't be found in refined women of the upper classes like Daisy, who is cool and ethereal. Myrtle dresses in strong colours: dark blue and brown, which contrast with Daisy's signature colour, white. Myrtle's rowdy drinks party in chapter two is like a caricature of Daisy's elegant dinner party in chapter one.
Myrtle is attracted to the handsome, powerful (physically and socially) Tom, and is immensely dissatisfied with her husband. She enjoys playing the 'lady of the manor' in the flat Tom rents for her:
'I told that boy about the ice.' Myrtle raised her eyebrows in despair at the shiftlessness of the lower orders.
However, Myrtle's pretentions are as ridiculous as the overlarge furniture with its
scenes of Versailles.
Myrtle is a victim of the selfish exploitation of the upper classes, but she is not a sympathetic character, being herself hard and heedless of others' feelings.