The woman Rep. Sheila Jackson Lee accused of racism is a celebrated photojournalist who helped document human-rights abuses in war-torn Guatemala during the 1980s.

Jean-Marie Simon, whose first-class seat on a United Airlines flight was given to Ms. Jackson Lee, Texas Democrat, lived and worked in Guatemala during the turbulent decade that saw the military seize control of the government in a coup. Hundreds of thousands of Guatemalans were killed or “disappeared” during the conflict.

Now a teacher, Ms. Simon, 63, is the author of “Guatemala: Eternal Spring Eternal Tyranny.” A 2012 blog post on Amnesty International saidMs. Simon donated 1,000 copies of her book to schools and universities in Guatemala “to keep the truth of what happened alive.”

In a tweet Tuesday, Ms. Jackson Lee suggested Ms. Simon was upset about her seat being given away because it was given to an “African-American woman.”

I noted that this individual came toward me and took a picture. I heard later that she might have said “I know who she is.” Since this was not any fault of mine, the way the individual continued to act appeared to be, upon reflection, because I was an African American woman, — Sheila Jackson Lee (@JacksonLeeTX18) December 26, 2017

In a Facebook post last week, Ms. Simon said her first-class ticket on a United Airlines flight from Houston to Washington, D.C., was given to Ms. Jackson Lee. She was on a return trip from Guatemala.

After bartering with Ms. Simon over the amount of the voucher she would receive as compensation, United eventually placed the disgruntled passenger in Economy Plus. The airline has yet to apologize for the incident.

“I was the last passenger on the plane,” Ms. Simon wrote on Facebook. “A Texas congressman, a nice guy, sat down next to me. He said was glad I had made it on the flight. I showed him my boarding pass with my seat, 1A, printed on it. He said, ‘You know what happened, right? Do you know who’s in your seat?’ I said no. He told me that it was Jackson Lee, a fellow U.S. congresswoman who regularly does this, that this was the third time he personally had watched her bump a passenger.”

Ms. Simon said during a delay before takeoff she went to the front of the plane and took a picture of Ms. Jackson Lee.

Ms. Jackson Lee said she did nothing wrong, but “in the spirit of the season and out of the sincerity of my heart, if it is perceived that I had anything to do with this, I am kind enough to simply say sorry.”