During her time in the Sejm, she served as a member of the social policy committee, as well as the labor market, family and women's rights subcommittees.

She became the Vice President of the PSL Executive Committee the following year, and in 2009 she was appointed as a Deputy MArshal of the Sejm, replacing Jarosław Kalinowski after he became a Member of the European Parliament.

After the 2011 parliamentary election, Kierzkowska was appointed a secretary of state under the Second Cabinet of Donald Tusk.

[2] She resigned from her position in the PSL shortly after the committee's 2012 election, which ousted Waldemar Pawlak in favor of Janusz Piechociński, after refusing to support Piechociński as the party's successor.

[3] Kierzkowska ran in the European parliament election in 2014 as a deputy for the PSL, and finished 7th out of 10 candidates with 633 votes.