Miss Baker, or Jordan Baker, is a childhood friend of Daisy's who is staying with the Buchanans for the summer at their home in East Egg. We first see her in Chapter 1, when Nick Carraway visits Daisy and Tom at their home for dinner and meets Miss Baker there.
Although Nick finds her attractive, he is also a bit fascinated by her because she looks familiar, yet he is sure that he's never met her before. Later on, he learns that she is the famous professional golfer, Jordan Baker, and he vaguely remembers some scandal that she was linked to in the newspapers. It had to do with a cheating incident that she was involved in during a golf tournament. This revelation, together with her professed carelessness whenever she found herself behind the wheel of a car, comes to have significance by the end of the novel, when Nick realizes that Daisy, Tom and even Jordan Baker all represent the careless people, who
" . . . smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made . . ."
Jordan Baker had a fleeting romantic interest in Nick, but it wasn't meant to last very long and it had ended long before the summer was over.