Myrtle feels tied to a husband she feels is dull and plodding. She is also tied to his financial state, which is modest at best. Her options are limited as is her horizon.
When Myrtle takes trips to New York with Tom, she is stepping out of one life and into another. In New York she has spending power. She is accompanied by a man of means. She can order around servants and fret over little things, acting out the role of the wealthy wife.
For Daisy, this behavior is always allowed. She was born into an upper-class home. Having servants is part of her life at all times. Daisy, unlike Myrtle, never leaves her world (the world of privilege) to visit other ways of being.
Daisy is like Myrtle in her feeling that she is tied into a marriage that is not fulfilling. The romance of her marriage seems to be gone and Daisy knows that Tom is having an affair. Myrtle makes sure that Daisy knows by calling at dinner time to speak to Tom.
Unlike Myrtle, Daisy has the option to leave Tom. George Wilson claimed to have the power to stop Myrtle from leaving him, but Tom never claims this power over Daisy. This power, for Daisy, parallels the relative power of her position as a person of means. Even without Tom, Daisy has money.
In the end, this privilege is starkly expressed in the facts of the narrative. Myrtle is killed and Daisy keeps driving, moving back to the midwest with impunity. Myrtle was exposed to the dangers of the world, where Daisy remained insulated from them.
Their lives are different in about every way imaginable. Myrtle is very poor and lives in a modest apartment above the garage her husband owns, where Daisy lives in a mansion on the bay. Mrytle comes from a lower middle class upbringing, while Daisy has always had money and would not know how to live without it. They are pretty much polar opposites.