Ivanka Trump said she could not remember property deals she handled at her father's firm, as she testified in a civil fraud case that threatens his business empire.
A judge has already found Donald Trump and two adult sons, Eric and Donald Jr, liable for fraud, ruling they inflated assets to secure favourable loans.
Ivanka Trump, 42, was initially a co-defendant, too, until an appeals court ruling in her favour this year.
She fought hard to avoid testifying.
The mother-of-three had argued she could not leave her children in Florida during a school week.
But a New York judge and appeals court ruled she must take the stand as a witness.
This is a non-jury trial, in which the judge will decide on allegations of falsifying business records, insurance fraud and conspiracy.
Mr Trump - the former US president and Republican frontrunner for next year's White House election - could be stripped of prized assets like Trump Tower. He and his sons deny wrongdoing.
New York Attorney General Letitia James, whose office filed the lawsuit, is seeking $250m (£204m) in fines and severe restrictions on how the Trump business operates in the state.
During four hours of testimony in the New York Supreme Court in lower Manhattan on Wednesday, Ms Trump spoke softly into the microphone, sitting upright with her hands in her lap, at times smiling brightly.
In composed and succinct responses, she repeatedly said she did not recall specifics, or was not aware.
Like her two brothers in their testimony last week, Ms Trump distanced herself from documents central to the case - her father's financial statements, in which assets were allegedly inflated to secure better loan deals.
"I wasn't involved in his statement of financial condition," Ms Trump said. "That would have been the company."
As they did with her brothers, lawyers for the state attorney general's office showed Ms Trump a series of emails meant to bolster their case, asking if she recognised the messages.
They pressed her on her role in securing loans from Deutsche Bank for the Trump National Doral Miami, the Old Post Office in Washington DC and Trump International Hotel & Tower Chicago.
At one point state attorneys produced an email she wrote to then-Trump Organization chief financial officer Allen Weisselberg about a loan.
"It doesn't get better than this," she wrote.
She said she did not remember that message.
Her responses frustrated Louis Solomon, the state lawyer questioning her.
"She just spent three minutes describing the plaza hotel," he shouted, "but she has no recollection when I ask her a question.
Defence lawyers began cross-examining Ms Trump in the afternoon, marking the first time they have questioned a Trump family member in this trial.
They asked her a series of direct questions about her role in company financial statements, to each of which she replied that she had no involvement at all.
The defence team also sought to portray a harmonious relationship between the Trumps and their loan provider, Deutsche Bank.
The Trump lawyers have previously argued that banks were happy to do business with the family and incurred no harm from the relationship.
Toward the end of the day, tensions began to flare as Judge Engoron argued the defence was wasting time, calling one Trump attorney Jesus Saurez's questions "ridiculous". Mr Suarez lost his temper after hearing the attorney general's team laugh at his questions from the bench behind him. The Trumps' legal team argued once again that the judge was biased for siding with prosecutors' objections to Mr Suarez's questioning. "Your constant insinuations that I have some sort of double standard…it's just not true," Mr Engoron said in response.
Nonetheless, University of Richmond law professor Carl Tobias told the BBC that Ms Trump's testimony was much less combative than her father's time on the witness stand on Monday.
And her evidence could ultimately aid the former president, said Prof Tobias.
"The attorney general's counsel was able to introduce some documents that appeared helpful to their case," he said.
"But counsel did not seem to elicit much information from Ms Trump's testimony that was very damaging to Mr Trump."
New York's attorney general said on the courthouse steps on Wednesday morning that Ivanka Trump was "very much involved" in the family enterprise.
From 2011-17, she was a top executive at the Trump Organization alongside her brothers Donald Jr and Eric.
As head of development and acquisitions, she played a key role in the types of real estate deals and loans at the heart of the case, say state attorneys.
The interest rates on the loans were low because they required a personal guarantee from Mr Trump and evidence of his liquidity and net worth.
State attorneys argue that Mr Trump's annual financial statements were central to those loans and saved him more than $100m.
Mr Trump has taken several times to his social media platform, Truth Social, to defend his children.
Hours before Ms Trump's testimony, he said his "wonderful and beautiful daughter" was being unfairly dragged into the case.
The trial is expected to last until mid-December.