What is Daisy's reaction to Myrtle's death?

Daisy is rattled by the crash but only as it pertains to Daisy. She easily accepts Gatsby's willingness to take the fall and claim he had been driving when it was Daisy driving. This is the turning point, the action, the pattern of Daisy's life--and Tom's too--and epitomizes their marriage and how they approach life. So Daisy's reaction has quickly entailed Tom's. They selfishly move from place to place renewing surface friendships or creating new ones, these relationships relying on their boredom. They are clearly not fulfilled but not searching to be. They amuse themselves with drinking. They roam from place to place making messes for the people around them and move on. Their pattern causes devastation around them. So Daisy slips into the pattern easily after the car crash, dumping Gatsby, turning to Tom as she believes he will fix the situation. They also seemingly get closer, Tom and Daisy. Their now more intense bond about how to get away from what they've caused assures, somewhat, Daisy. Think of the scene where, through a window, we see them sitting at their kitchen table intensely talking about, we assume, their plan to leave, quickly, their current circumstances. In the end, Daisy's reaction is about her concern for herself, not Gatsby, not Myrtle, not the life Tom and Daisy have built, albeit a terribly surface one.

From the description of the accident that Gatsby gives Nick, the reader is meant to infer that she was distraught prior to the accident and after it as well. Shortly after, Fitzgerald paints an entirely different picture; this picture containing Tom and Daisy huddled together not happy nor sad but with conspiring looks. It is clear to the reader that Daisy simply wants to avoid facing the situation, similar to how she deals with any real conflict in the novel. Tom leads George to believe that Gatsby is responsible for Myrtle's death, ultimately leading him to his death. Tom and Daisy ruin the lives of many people in the novel. Without a care in the world, they both disappear to live their comfortably unhappy lives.

Daisy is at first shaken up by Myrtle Wilson's death, which of course she caused—she was driving the car that hit Myrtle outside her house. But beyond her initial reaction, her response to Myrtle's death is to completely wash her hands of it. She allows Gatsby to take the blame for the killing and never acknowledges responsibility herself. This, along with the fact that Tom allows Mr. Wilson to believe that Gatsby was actually having an affair with Myrtle, leads to Gatsby's death. Daisy suffers no visible consequences for Myrtle's death. She goes back to Tom, and together the two of them leave. As Nick says, Daisy, like her husband, is "careless." She, as much as Tom, wrecks the lives of the people she comes across and leaves them to suffer the consequences, "retreating back into their money or their vast carelessness, or whatever it was that kept them together." They destroy the Wilsons as well as Gatsby.