Trump, who has denied having an affair with Daniels, is seeking the Republican nomination for the presidency in 2024.
"Stormy responded to questions and has agreed to make herself available as a witness, or for further inquiry if needed," Clark Brewster, Daniels' lawyer, wrote on Twitter.
Susan Necheles, a lawyer for Trump, did not immediately respond to a request for comment on Daniels' talks with prosecutors.
Joseph Tacopina, another Trump lawyer, said earlier this week Trump did not plan to appear before the grand jury, but that a decision had not yet been made.
The investigation centers on a $130,000 payment Daniels - whose real name is Stephanie Clifford - received in October 2016 from Michael Cohen, Trump's former personal attorney and fixer.