Washington (CNN) Fiona Hill , President Donald Trump's former top Russia adviser, testified publicly on Thursday before the House Intelligence Committee in the Democratic-led impeachment inquiry into President Donald Trump.

Hill, a former national security adviser until she left the administration this summer, told lawmakers that US Ambassador to the European Union Gordon Sondland was involved in a "domestic political errand" in Ukraine, while she and others were trying to stay involved in "national security foreign policy."

She told Congress that it was obvious to her that when Trump's aides mentioned "Burisma," a Ukrainian energy company, that they were really thinking about former Vice President Joe Biden.

And she forcefully rejected and dismantled the notion that Ukraine meddled in the 2016 election to harm Trump, calling it a "fictional narrative that has been perpetrated and propagated by the Russian security services themselves."

Time in the administration

In April 2017, Hill took a leave of absence from the Brookings Institution to join the Trump administration, lending her extensive knowledge and expertise on Russia as the deputy assistant to the President and senior director for European and Russian Affairs.

She was initially hired by former national security adviser Gen. Michael Flynn, his then-deputy KT McFarland, and then-chief of staff to the National Security Council Lt. Gen. Keith Kellogg.

"I -- and they -- thought I could help them with President Trump's stated goal of improving relations with Russia, while still implementing policies designed to deter Russian conduct that threatens the United States, including the unprecedented and successful Russian operation to interfere in the 2016 presidential election," Hill recounted Thursday.

During her time with the National Security Council, she oversaw rocky Washington-Moscow ties, and her views sometimes seemed at odds with Trump's desire to improve relations with Russian President Vladimir Putin who he has praised on multiple occasions.

According to The Washington Post , Hill's relationship with Trump got off to a rocky start. During a meeting prepping for a call with Putin, Trump mistook Hill for a member of his clerical staff and instructed her to rewrite a memo, which led Hill to respond with a "perplexed look," officials recounted to the newspaper. Trump was irritated by the exchange and told then-national security adviser H.R. McMaster to intervene, the Post reported.

Hill accompanied Trump to the 2017 G20 meeting, though she was left out of Trump's first formal meeting with Putin. The Post reported in January that Hill had sought more information beyond a readout of the meeting, which Trump had instructed his interpreter not to speak about and had taken the interpreter's notes.

And she traveled with Trump to Helsinki last year for his infamous summit with Putin , where he appeared to side with the Russian strongman over his US intelligence community.

The former adviser testified before Congress last month that she officially turned in her badge in September, though she had handed over most of her responsibilities in July. Her departure in July came about a week before Trump's call with Zelensky that prompted the whistleblower complaint alleging Trump abused his office by soliciting "interference" from a foreign country in the 2020 presidential campaign.

Decades of studying Russia

A critical biographer of Putin, Hill has authored or co-authored a number of books on Russia, including two editions of a book titled "Mr. Putin: Operative in the Kremlin."

"From the KGB to the Kremlin: a multidimensional portrait of the man at war with the West," a description of the book reads.

From 2009 to 2017, Hill did a long stint at the Brookings Institution, where she directed the Center on the United States and Europe.

Before joining the think tank, Hill worked in the US intelligence community under former Presidents George W. Bush and Barack Obama. She served as a national intelligence officer for Russia and Eurasia with the National Intelligence Council for three years.

She also oversaw strategic planning at The Eurasia Foundation, a nonprofit supported by USAID that was born out of an effort to help former Soviet Union nations.

Hill testified that she began her university studies in 1984. She holds a master's in Russian and modern history from St. Andrews University in Scotland, spending some time studying in Moscow.

During the 90s , she held a number of roles directing research at Harvard University's John F. Kennedy School of Government, while she completed a master's in Soviet studies and a doctorate in history.

'American by choice'

During her testimony on Thursday, Hill shared that she grew up in the northeast of England -- the same region that George Washington's ancestors came from.

"The men in my father's family were coalminers whose families always struggled with poverty," Hill said, adding that her father started working in the mines at 14 "to help put food on the table."

When the local mines closed in the 1960s, her father, who "loved America, its culture, its history and its role as a beacon of hope," had dreams of emigrating to the US, but stayed in England to care for his mother, who was in poor health.

Hill made clear that America "has offered for me opportunities I never would have had in England."

She said she "grew up poor with a very distinctive working-class accent " that would have "impeded my professional advancement" in England.

"I am an American by choice," said Hill, who became a naturalized US citizen in 2002.

She also confirmed an anecdote that had been reported by The New York Times that when she was 11, a school boy in her class set fire to one of her pigtails while she was taking a test. She put the fire out with her hands and continued finishing the exam.

Hill said the incident resulted in her mother giving her a bowl haircut and joked that she ended up looking like King Richard III in her school pictures.

This story was updated with additional information after Fiona Hill's testimony.