[3][10] On July 22, she was nominated by President Trump to serve concurrent five-year appointments as chairperson and CEO of CSB.

[13][14] A hearing on her nomination was held by the United States Senate Committee on Environment and Public Works in September 2019.

[21] A July 2020 Environmental Protection Agency Office of Inspector General report concluded that it remained an open question whether a single CSB board member may constitute a quorum, as doing so would impair the segregation of duties mandated by the Government Accountability Office.

[21][22] In May 2021, Public Employees for Environmental Responsibility criticized Lemos for accruing $33,000 in travel expenses and $20,000 in office renovations, and for hiring a senior advisor from Northrop Grumman for an undisclosed salary.

[23][24] In a September 2021 hearing before the United States House Energy Subcommittee on Oversight and Investigations, Lemos testified that the CSB is "on an upward trend".

[24] Lemos submitted her letter of resignation to the White House in June 2022, citing lost confidence in the board's focus on the agency's mission.

[28][29] Senator Chuck Grassley wrote a letter to Lemos requesting that she repay the money indicated as improperly spent in the report.