What prompted this:
That she realized Tom's words, and that
she could never leave her husband for
Gatsby.
Step-by-step explanation:
Daisy had a great love for Gatsby but the
fact that Tom had singled him out as a
common bootlegger made her realize the
consequences this would bring.
She was actually scared by those words
which caused her to stay with Tom even
though she didn't love him.
All this happens in the discussion that
Tom and Gatsby have where they fight for
the love of Daisy, and that's where Tom
reveals about the investigation he made
about Gatsby and his drugstores, which
leaves Daisy terrified, and realizes that
Gatbsy couldn't win the confrontation.