The scene that addresses your question appears in Chapter VII during Gatsby's confrontation with Tom Buchanan in the hotel room in New York. Gatsby declares his and Daisy's love for each other and says she is leaving Tom. Buchanan responds by reminding Daisy of some tender moments they shared in their marriage and by attacking Gatsby, showing him up to be a cheap criminal. Daisy is caught in the middle as the two men in her life fight for her. She cannot say she never loved Tom, as Gatsby insists, but considering Tom's many infidelities, she finds his sudden professions of love to be "revolting." Nick observes that Daisy "was staring terrified between Gatsby and her husband."
As Tom's rant against Gatsby continues and as Gatsby tries to defend himself against Tom's accusations, Daisy withdraws "further and further into herself," finally begging Tom to stop:
"Please, Tom! I can't stand this any more."
Her frightened eyes told that whatever intentions, whatever courage she had had, were definitely gone.
When forced to decide between her marriage with Tom and her romantic affair with Gatsby, Daisy cannot take a firm stand and state her intentions. Instead she simply withdraws, leaving New York in Gatsby's car as Tom directs her to do in a display of ego showing his disdain for any relationship Gatsby believes he has with Daisy.
As Gatsby later recounts events to Nick, Daisy drove his car on the way home because she was "very nervous and she thought it would steady her to drive." In her disturbed emotional state, she runs over Myrtle Wilson, killing her, and does not stop. Daisy's leaving the scene of the accident in Gatsby's car leads to George Wilson's shooting Gatsby and then killing himself. Daisy's weakness in managing her own life results in the deaths of three people.