Hicks, who up until March 2018 was one of Trump's closest advisers, appeared before the Democratic-controlled House Judiciary Committee in a closed-door session on Wednesday, Efe news reported.
That panel is investigating whether Trump obstructed justice during the two-year independent probe by Special Counsel Robert Mueller of his 2016 campaign's links and contacts with Russia.
Mueller wrapped up his probe earlier this year and issued a 400-plus page report on his findings, which included possible instances of Trump's obstruction of justice although the special counsel did not bring any criminal charges against the President, saying that to do so against a sitting president would be unconstitutional.
He left to Congress the task of pursuing any further investigations into whether or not to impeach Trump for high crimes or misdemeanors.
But Hicks refused to respond to questions related to her time in the White House and on Trump's transition team after he won the 2016 election, and she only answered questions related to the presidential campaign, according to lawmakers from both parties consulted by The New York Times.
Hicks cited Trump's instructions that, she said, give her "absolute immunity" from the obligation to answer lawmakers' questions about her White House tenure, according to the daily.
In fact, she appeared before the House committee with a letter from White House counsel Pat Cipollone stating that Trump directed Hicks not to answer any questions "relating to the time of her service as a senior adviser to the president".
( With inputs from IANS )