In Chapter Six of Fitzgerald's The Great Gatsby, the segment quoted, "Daisy's voice was playing murmurous tricks in her throat," brings to my mind that Daisy is simply playing with the sound of her voice—she's acting.
Daisy has never impressed me as a person of any depth, but simply someone who enjoys having fun, spending money, and living in the midst of wealth—with no desire to assume responsibility for anything. Her daughter is taken care of for her: Daisy has little time to devote to her child. In fact, the youngster is more like Daisy's doll than her daughter. When Gatsby and Tom argue over her, Daisy refuses to choose between them, as if it would be uncomfortable to face doing anything whereby she has to take a stand. Even after Gatsby is killed by Myrtle's husband (when Gatsby has taken Daisy's blame for Myrtle's death upon himself), Daisy isn't decent enough to go to Gatsby's funeral.
In essence, Daisy is shallow, childish and spoiled. When she and Tom come to Gatsby's party, she is enchanted by how many well-known people there are there. Though one man is identified as only a "small producer," Daisy is still impressed by him (with nothing other to commend him except his connection with films...it would seem):
Gatsby identified him, adding that he was a small producer.
"Well, I liked him anyhow."
The movie star and her director fascinate Daisy. In seeing the "moving picture director and his Star," Daisy comments:
I like her...I think she's lovely.
The two women have not spoken; we might infer that Daisy approves of the woman because of her fame, her beauty, her seeming wealth, or perhaps because these people are kindred spirits: creating and living in dream worlds.
In studying Daisy throughout the story, we find little to admire: she flirts with Gatsby (who seems deeply in love with her, though he is also quite a bit unrealistic in his expectations), but thinks nothing of dismissing him out of hand. She wants to be with Gatsby unless it becomes uncomfortable for her. She...
...never loses interest in the illusion of her love with Gatsby.
When Daisy arrives at the party, I think she is playing with her voice. She is like a child playing dress-up. Changing her voice (I believe) is a game to her. I think she is playing with her voice to see how she can make it sound...as if she is playing a part. For her remarks to her cousin (Nick) thereafter seem ridiculous—not based in reality at all:
"These things excite me so," she whispered. "If you want to kiss me anytime during the evening, Nick, just let me know and I'll be glad to arrange it for you."
Daisy is pretending; she is playing a part: that of a wife and mother, a wealthy woman, and a lovely creature who has been greatly sought after by men all her adult life. It's all superficial, and when she plays with her voice—and offers to arrange the opportunity for a kiss with Nick—this all seems like part of the dream world in which she exists. This world does not concede that she is married to a man who cheats on her or that her marriage seems to have been a mistake. Though having a life with Gatsby is totally unrealistic, she does not send him away. And in her dream world, her responsibility as a parent does not exist. For Daisy, it's all about pretense and living out her version of the American Dream.